15,000 visitors attended the event at Hatfield House

The event in Hertfordshire - run by Thomas brand owner Hit Entertainment - was a 15,000 sell-out, with some �10 tickets fetching 20 times their value.

Charles Burdick, chief executive officer, said they were taking complaints very seriously.

He promised a full investigation into the event at Hatfield House.

We apologise for any disappointment caused to visitors at Saturday's event Charles Burdick, of Hit Entertainment

"We are aware that there were a number of disappointed visitors to the Thomas 60th anniversary celebration on Saturday," he said.

He added: "A full investigation is under way but without the opportunity to review comments from visitors, we are unable to make a full statement at this point."

A special email address has been set up for comments from visitors to Saturday's event, which is thomas60th@hitentertainment.com.

The company will also be setting up a special telephone line where comments can be left along with the callers' names and addresses. Details of the phone line will be posted on the Thomas website.

A 'letdown'

Mr Burdick said: "All emails and telephone messages will be replied to. We apologise for any disappointment caused to visitors at Saturday's event."

London-based Hit Entertainment's leaflets promoted the party as "an opportunity to climb aboard for hours of fun and the chance to the meet everyone's favourite Number 1 Blue Engine".

Tony Goose, 34, of Southend, Essex, said the event was a letdown and would only describe it as a funfair with queues.

Grandfather Trevor Fountaine, of King's Lynn, Norfolk, travelled 90 miles to take his two small grandchildren to the event.

"We thought we were taking them to see Thomas the Tank Engine. He was not there. It was like a church garden fete. Children were saying where is Thomas the Tank?"