Passengers are being warned to expect huge delays at UK airports on Wednesday following the news that a strike by public sector workers will definitely go ahead.Travellers face long queues and overcrowding when border staff join a mass strike over planned reforms to public sector pensions.Delays at Heathrow could last as long as 12 hours and airlines were warned of ‘mass cancellations’ of departing aircraft.Passengers arriving on international flights into London or transferring through London onto a domestic flight will be hit, but those departing from the capital or travelling on UK domestic flights will be unaffected.Airports operator BAA has asked airlines to halve the number of international passengers flying into Britain on Wednesday in order to minimise the delays and the UK Border Agency (UKBA) has been seeking volunteers from other parts of the civil service to cover for the strikers.