The shock resignation of London Ambulance Service trust chief executive Michael Honey has sparked speculation that he was forced out for failing to win adequate funding for the service.

Mr Honey agreed to leave the trust last week, following what a statement described as 'personal and private' discussions with chair Sigurd Reinton.

In the statement, Mr Honey said he was 'proud' to have seen the service through four difficult years. 'There is still much to be done and I hope the work that has now started in negotiating extra money for the LAS to cope with increasing demand will bear fruit.'

Mr Reinton, formerly chair of Mayday Healthcare trust in Croydon, praised Mr Honey for his hard work during a period of major change.

The sudden departure of the chief executive, who gives up a salary package worth£110,000 a year, took observers by surprise. John Lister, information director of London Health Emergency, said: 'It's a move out of the blue.

'There's no evidence that the problems of the LAS are down to Michael Honey - they are due to LAS not having the resources to cope with growing demand.

'If I've got a criticism of Honey it's that he attempted to make things look rosier than they are rather than confront the scale of the problems.'

Unison's regional organiser for London, Phil Thompson, said Mr Honey could have paid the price for his one 'failure'. 'He has not been successful in obtaining sufficient resources for the service. If you are paying someone£100,000-plus a year they have, ultimately, to accept responsibility for a service not meeting its targets.'

Elizabeth Manero, chair of London Healthlink, the umbrella organisation for the capital's community health councils, also identified funding as a key issue.

'If the main issue is funding, then it needs someone who can really thump the table.'

Mr Honey, an architect by training, was chief executive of Gloucestershire county council for five years and had no NHS experience before joining LAS in 1996.

His appointment to the top job at the trust stunned ambulance managers, who had expected incumbent head of service Martin Gorham to get it. But Mr Honey appeared to have won round sceptics and was widely viewed as an intelligent and effective manager.

LAS and the Department of Health refused to comment further on the reasons for Mr Honey's departure.

Director of operations Peter Bradley has been appointed acting chief executive.

In January, LAS reached 90 per cent of emergency calls within 14 minutes, and 53 per cent within eight minutes, compared with national targets of 95 per cent and 50 per cent. Over the past 10 years, demand has risen by 50 per cent.