Henry was born on 23rd January 1893 in Walthamstow, Essex, the eldest of three children of the Rev. Henry Alfred and Alice Mary Allpass of Heydor, Endlebury Road, Chingford, Essex.

He was educated at Chigwell School in Essex and then went to Exeter College, Oxford where he was a member of a small club, co-founded by J. R. R. Tolkein, called the 'Apolausticks'. He was also a member of the Fabian Society and described as 'the best topical poet in Oxford.'

He won first class honours in the final school of modern languages at Oxford in 1914 and later that year was appointed as senior modern language master at St. Bees School, Cumberland where he was also in the OTC.

In December 1915 he transferred to the Essex Regiment, and in June 1916 he volunteered for service in France with the 1st Battalion of the Cambridgeshire Regiment, and was appointed as battalion bombing officer. He was recommended by his colonel for the Military Cross for 'most gallant behaviour under fire.'

He was noted as having an exceptional gift of literary expression in prose and verse, combined as it was with an astonishing fertility of ideas. Much of his best work was written at various times for the Westminster Gazette, for the Isis during his undergraduate days, and for Stars, a camp paper which he himself edited during his period of training with the Essex Regiment.

He was reported missing after leading a bombing raid on German trenches near Hamel on 16 September 1916, aged 23. 

Although he was too badly wounded to move and stretcher-bearers were unable to get to him, he was seen within the German wire, and there seemed to be good reason and hope he was still alive and a prisoner. But nothing more was heard from him.

He is also commemorated on the Chingford War Memorial.

Following his death a collection of his verse and prose was published as Oxford, St. Bees and the Front which included this poem:

HONOUR TO WHOM HONOUR

When dim in the far time,
It shall not be war-time
And life be not death, and pleasures increase;
When dazzle the cheering,
And the end of the fearing
And the manifold blessings of Commerce and Peace.

When pulpits are crowing,
And wine is a-flowing,
And friends are a-meeting who long have not met;
When fair is Earth’s promise,
And you patronise ‘Tommies’ –

In the day of rejoicing you shall not forget:
‘Tis Ours that you’re reaping,
Ours who lie sleeping,
Princes of Ypres and Loos and the Aisne:
To us be the glory,
Us, mangled and gory,
First honour to Us, whom you honour in vain.

Then, sorrowing greatly,
Your Jubilee stately
You shall keep fast to the friends who are fled,
And solemnly voicing
Shall cease you rejoicing
To toast and keep toasting the health of THE DEAD.

His brother Second Lieutenant Edmond Theodore Allpass, 9th Battalion, Sherwood Foresters (Notts and Derby Regiment), predeceased him. Edmond died on 21st August 1915, aged 20, serving at Gallipoli. He is commemorated on the Helles Memorial in Turkey.