I submitted an EU261 claim on BA's web site the day after the flight for the £95 cost of Addison Lee from LHR to home (near LCY). BA initially refused, stating "We’ve refused your claim for compensation because we told you about the cancellation at least 14 days before you were due to depart, using the contact details in your booking. Under EU legislation, we aren’t liable to pay compensation or cover additional costs for this kind of situation".
Of course, this is incorrect, because two weeks’ notice exempts airlines only from Articles 5(1)(c) and 7 of Regulation (EC) No 261/2004 regarding statutory compensation (€250, €400, €600, £220, £350 or £520).
I therefore asked BA to quote the article of the legislation on which it was relying. Instead of arguing the same legal point again, I repeatedly asked for BA's final response, so I could complain to CEDR. After a further reply, BA conceded and today notified me that I will receive the £95 in my bank account within 21 days. I get the impression that BA routinely refuses these claims because most consumers don't know their rights.
There were fortunately no immigration delays after landing at LHR.