Ken Livingstone, the mayor of London, came under criticism yesterday after raising the prospect of a £5-a-time charge to drive to Heathrow by 2005.

Mr Livingstone said he wanted to tackle the problem of so-called "kiss and fly", where people get family members to drive to the airport to drop them off.

Angie Bray, the London assembly's Conservative spokeswoman on congestion charging, said this was inhumane: "Many families with roots outside the UK are constantly seeing off loved ones at Heathrow and the airport check-in desk will be the last time families see each other for a long period. That Livingstone wants to charge people to say goodbye to loved ones is fundamentally wrong."

But the Tory candidate for mayor of London, Steve Norris, has backtracked on his promise to scrap congestion charging, just two months after pledging that it would be the central plank of his campaign.

Following the smooth introduction of the £5-a-day charge in February, Mr Norris admitted this week in trade magazine Traffic Technology International that he was having second thoughts about axing it - which would cost £81m.

His remarks represented a sharp change from his stance eight weeks ago when he referred to the charge as "a massive political gesture founded on an unjustified principle".