Ciao Eleuterio,

i hope this answer doesn't come too late.

In England is much different than in Italy: professional relationships are mainly based on honesty and straightforwardness.

If both companies offer you a job, you just have to tell the one you decide to decline, that "thanks but i received a better offer". Put it down nicely (the brits love honest people but also love to use nice words even for the worst messages ) and thank them a lot. They're not gonna black list you and they're not going to call all their friends to tell them you're a pr*ck and not to offer you a job ever again.

in bocca al lupo!