You want £100??

Well good luck with that. You simply won't get that from them.

it is out if all proportion to the fare you paid. Out of the £800 for your return flights
a fair chunk was BA passing onto you various airport and government charges e.g ~£70 in APD, ~£40 for LHR fees plus whatever the Canadians charge.

From my experience £20 - £25 in vouchers is the standard offer of a number of airlines for a non working IFE. Maybe they thought you were only claiming for yourself and not for your partner?

Was it annoying the IFE didn't work yes of course it was but you won't do yourself any favours by asking for an unrealistic amount.