The weather is bad, the nights are still long and your Christmas overspending has finally caught up with you.

On top of that your New Year resolution to give up smoking has just gone out of the window as you strive to cope with the pressures of having gone back to work after the holiday break.

So welcome to "Blue Monday" - Monday, 22 January - officially designated by a psychologist as the most depressing day of the year. It has been singled out by Dr Cliff Arnall, psychologist and former tutor at Cardiff University, who has used mathematical equations to reach his verdict.

He worked out that people are most likely to get the blues in the final full week of January because of the combination of bad weather, Christmas debts and broken New Year resolutions. There seems to be some backing for his theory, too.

Phillip Hodson, a fellow of the British Association for Counselling, said: "The worst day has got to be a Monday - there is other evidence to show it is the worst day of the week.

"Our bodies work on a 25-hour clock so that - by the time we get to the weekend - we stay up later. That makes it difficult for us to go to sleep on Sunday and we wake up grumpy.

"It's also got to be around this time of year - we are less contented with our body image because we've been bingeing."

Samaritans spokeswoman Kate Redway added: "Sadly one in five people in the UK experiences depression and this time of year can be particularly difficult, with people in debt after Christmas and finding it hard to settle back into a work routine during dark days."

And the forecast gets gloomier. Meteorologists were last night predicting the worst weather of the winter - with snow, sleet and hail hitting most parts of the UK, as the unseasonably mild temperatures plummet. MeteoGroup forecaster Michael Dukes said: "Temperatures are going to plummet - there could be snow almost anywhere."

Happily help is at hand, though, and there has even been a website set up solely for the purpose of beating the blues this Monday morning - www.beatbluemonday.org.uk.

Suggestions posted on it include: do some exercise, talk to someone about your problems, sit down with a good book and a glass of wine, go for a walk in the country or go for a run - you will feel a sense of achievement if you manage a mile. Of course, not everyone subscribes to the theory that today will be the bluest day of the year.

Newspaper "agony aunt" Virginia Ironside admitted: "I think there is a general assumption that we all feel a little glum after Christmas. But I'm not sure it can be justified to pick out just this one day. The idea that it is the weather and money that makes you feel depressed - I think that is a little crass." However, she said there could be something to be said for officially designating the day "Blue Monday".

"When one is depressed, one is so enveloped with the idea that nobody else in the world is as depressed as you," she said. "It's quite nice there is a day when you realise other people feel depressed and feel just as bad as you. It might help you feel better."

The other advantage of having one day identified as being the worst in the year for depression is that it might make people feel good when they get through it and wake up on Tuesday morning, other experts argued.

Dr Stephen Joseph a psychologist at the University of Warwick, backed Dr Arnall's theory. "I haven't come across the idea before," he said, "but I think there is a seasonal effect on people. It's an interesting theory." Dr Joseph has been engaged in a study aimed at finding out how people can achieve happiness. His advice to those feeling the blues this morning was for them to "practice gratitude exercises".

"Sit down for about 15 minutes and write, say, three reasons why you should be feeling grateful," he said. "For instance, you could say you are grateful for your friends and the time you have spent with them, you are grateful for your health, grateful for that Christmas gift you received last month.

"There are a number of experimental studies which show that gratitude exercises - spending a little time of the day thinking about things you should be grateful for - can lift people's moods in the long term. They do get happier.

"It's a very important thing and - if there was one message that I'd like people to take today to help them - it is to spend some time on this positive type of thinking. People who do it often do it for far longer than the period of the exercise - and feel happier as a result."

If you want an hour-by-hour blueprint showing you how to get through the day, why not try the following? Start the day with a good breakfast because, according to nutritional expert Fiona Hunter, that can help put you in a good mood.

"A healthy, balanced breakfast helps set you up for the day ahead in more ways that one," she said. "It reduces stress levels and helps you think straight by boosting concentration and mental performance to help cope with the morning rush. It prevents depression and mood swings."

Once on the road to work, the RAC Foundation has come up with a series of measures to continue the battle against the blues.

These include focussing on doing stretches and shoulder exercises if stuck at traffic lights - rather than gnashing their teeth at other motorists and shouting at them.

It is calling on them generally to relax by allowing fellow drivers into spaces instead of competing with them - or work from home if at all possible.

"We hope motorists will rise to the challenge of 'beat blue Monday' day and find ways of beating the commuting blues," said the foundation's chief executive Edmund King.

"Travelling smarter rather than longer is part of the answer, while putting a great song on the stereo is a proven mood-lifter."

(NB: Songs you should avoid are "Monday, Monday by the Mamas and the Papas and "I Don't Like Mondays" by the Boomtown Rats.)

Then, at the office, why not deck the place out to make it look a little brighter?

You could take a leaf out of PR consultancy Green Communications' book. Today they are decking their offices out as a beach complete with sand and deck-chairs for the staff to conjure up an image of summer aimed at making employees feel better.

During the rest of the day, the Church of England has some interesting tips for Lent which you could employ to enable you to feel a glow - such as leave money in a shopping trolley for someone else to find or give up your place in a queue to someone in a rush.

Once back home again and the advice from the blogger on the www.beatmondayblues.org.uk site who says: "I find that sitting down with a good book and a glass of wine always cheers me up" could come into effect.

Before you know it, it will be Tuesday.

Ten ways to beat the blues

1 Make sure you get up, get dressed and try to look good - don't leave off make-up.

2 Make a list of those you know, and how you affect their lives in a positive way.

3 Exercise - it can change your mood.

4 Remember it is "Blue Monday" - you are not the only one feeling blue.

5 Indulge in a gratification exercise - take 15 minutes to write three things you are grateful for such as your health, Christmas presents and friends.

6 Buy a light box - this can help those driven to depression in winter by lack of light.

7 Try to be more disciplined with your bed-times

8 Think like the Opposition party - ie from a different point of view.

9 Try a good book and a glass of wine.

10 Visit Australia (it's lighter).