In northern France and Flanders, troops were locked in a brutal struggle after more than two years of conflict.

But while thousands fought courageously on the battlefields of the Western Front in 1917, a birthday card was handed over by British soldiers that has now sparked a 95-year-old mystery.

And it is a wartime conundrum which a Kessingland woman is determined to solve.

Anita Guymer, 49, recently found the card which was given to her grandfather Stanley Rosindale on January 4, 1917, more than two years after the outbreak of the first world war.

It was signed by more than 130 members of the 'casualty branch GHQ, 3rd ech B.E.F' and bears the message: 'Heartiest congratulations to Rosi on his twenty-first. With best wishes for a bright and happy birthday and so on for many years to come'.

It is believed the B.E.F refers to the British Expeditionary Force which fought the Germans in brutal trench warfare.

One of the dozens of names on the card is that of a member of the 8th Hussars.

However, for Mrs Guymer, the discovery of the birthday card has created a mystery as she never knew her grandfather, who lived in Romford in Essex and died in 1972.

Until she found it, she had no idea he had any military connections or that he might have been involved with the forces in the first world war.

Mrs Guymer, a medical secretary, found the birthday greeting when she was going through the belongings of her late father, Philip Rosindale, who lived in Oulton Broad and died in April, aged 78.

It was among a set of newspapers from the 1930s, including issues from Essex and Yorkshire.

Mrs Guymer, of Church Road, Kessingland, said: 'The card was actually in the bottom of my father's wardrobe. It was just lying on the bottom of it. At first I was going to chuck it away.

'But then I had another look and realised it was for my grandfather. It is all a bit of a mystery as I did not know that my grandfather was in the army or involved in world war one; I just knew he was a civil servant with BP.'

To try to find out more about the birthday card – and her grandfather's life and military service – Mrs Guymer has sent a copy to the Imperial War Museum in London, which is now investigating.

Mrs Guymer, a mother-of-two who went to St Mary's School in Lowestoft, said: 'I just want to know why it was given to him and where it was given to him.

'It would be nice to find out more about him. He was a kind and quiet man.'

Mrs Guymer's father Philip was an electrician and was member of the Knights of St Columba, a fraternal organisation of Catholic gentlemen, founded in Glasgow in 1919.

A spokesman for the Imperial War Museum said its documents department had only just received the card and once it was able to shed any light on its origins, it would contact Mrs Guymer straight away.

anthony.carroll@archant.co.uk