The Untold Battle of Trafalgar, Channel 4

If you happen to be in Trafalgar Square in London any time soon, you should take a close look at the friezes that adorn the ground portion of Nelson’s Column. For there you will find, most unexpectedly, that one of the sailors depicted is a black man, one of 1,400 non-British seamen among the 18,000 who took part in the Battle of Trafalgar on 21 October, 1805.

That striking factoid comes from The Untold Battle of Trafalgar, the first in a four-part season, Bloody Foreigners on Channel 4, which aims to show how foreigners were at the heart of some of Britain’s most important historic events. It’s an alluring come-on - who wouldn’t tune in for that? - and this film began by promising to show how the 25 nationalities who were part of Nelson’s fleet that day helped to make Britain the world’s greatest naval power for the next 100 years or so. In actuality, it told a much more intimate story - that of the foreigners onboard one of Nelson’s ships, HMS Bellerophon (Billy Ruffian to her crew).

The film’s documentary evidence was the diary kept by one of Bellerophon’s officers and ships’ documents (now kept at the National Maritime Museum in London), which show some remarkably - and unusually, for the time - detailed information about her crew, including their ethnic origins. Nationalities on board were American, French, Swedish, West Indian, Portuguese and Indian, and the crew included 10 black men, who were, as far as we can tell, treated just the same as anybody else. As Jeremy Hardy’s film was keen to point out, this makes Nelson’s navy the first equal opportunities employer.

Academics made educated guesses about how the non-Britons came to serve in the British Navy - variously they were press-ganged, were escaped slaves, had fled the French Revolution or were offered freedom from prisoner-of-war status if they joined up - and Hardy used dramatic re-enactments to show their roles onboard on that fateful day in 1805 when HMS Bellerophon, as part of the British fleet, faced the combined might of the French and Spanish navies.

But it was unlikely that few, if any, of the sailors involved, whether British or foreign, were there entirely out of a sense of duty to king and country. Rather they were probably thinking of retiring immediately after the battle because the British government had introduced the country’s first bonus scheme - the “prize” money the sailors of all ranks would earn when they brought into port a taken French or Spanish ship. Even for the lowliest sailor it would amount to a small fortune.

Sadly for those on board HMS Bellerophon, then, the ravaging storms that immediately followed the Battle of Trafalgar meant that the prize was much reduced because only four of the 19 taken ships reached the British home port of Gibraltar. The amounts settled on the ordinary seamen were so paltry that after a public outcry the government was forced to increase the payments, but they were still pittances in most cases.

But however fascinating the story of those aboard the Bellerophon that day when England expected every man to do his duty, this film didn’t fulfil its opening promise to tell the much bigger story of foreigners’ contribution to one of the most audacious naval victories in history. This film had the hallmark of something being made to fit into a themed series, however loosely it fitted the criteria, and I felt rather cheated. I hope the films that follow deliver more.

• Bloody Foreigners continues on Channel 4 nightly until Thursday