Advice to those claiming compensation – always quote EU 261/2004 in your correspondence.
There is an instance noted on FlyerTalk where BA has offered compensation of £100 (£50 each for two people) in the form of e-vouchers, redeemable only with BA, that cannot be used in conjunction with Avios or points, and which expire within one year.
In the case above, the wait was for over 3 hours.
Quoting EU 261 should result in compensation in line with the directive which appears to be considerably more than the prevailing BA view. It also avoids you getting stuck with a rather restrictive e-voucher which you may not wish to use.