Giving Eurostar tickets to another person

Not likely....if I remember correctly, they check passengers' ID against the name on the ticket.

Frequently you just have to play the odds and, sometimes, you lose. At least you didn't lose much. I play those odds all the time. They do check your ID so no another person can't use it (which is good when you think about it...a ticket pinched from your pocket is useless to someone else). Anyway, I presume you didn't take out travel insurance (TravelGuard et. al.) because if you did and you had to cancel for medical reasons etc. you're entitled to a refund if you paid the small sum extra for that coverage. I'm a big fan of travel insurance (minimum cost to cover air fare, medical evac etc.). Still, I wing in on this sort of thing and what I get would not cover a charge this small.

Eurostar is the most secure rail line in Europe. It has airline style check in, in fact I recall standing in line to pass through French ticketing, then a French document check, then a British document check...all before getting on the train. At the other end, another British document check and a security check...so if passport and tickets do not match...I think it would be an issue.