Long-running archaeology series Time Team has been axed by Channel Four following falling ratings and accusations that the show was dumbing down.

The series which is presented by Tony Robinson has been on air since 1994 and has unearthed historical relics ranging from the remains of the first Spitfire to be shot down during the Battle of Britain to skeletons of Anglo-Saxon monks beneath Westminster Abbey.

Robinson, who played the faithful but idiotic Baldrick in Blackadder, said: “Not many performers are given the privilege of featuring in two iconic TV series – but I've been lucky."

"Time Team was not only high-quality public service television, it also attracted a large and passionate audience both in the UK and overseas. I'm proud to have been associated with it."

The show has been exported to more than 36 countries and up until four years ago had been attracting 2.5 million viewers, but recent series have lost viewers.

According to a report in today's Guardian, a revamp to boost ratings was criticised by one of the show's regular experts, Mick Aston, who left, claiming it had been "dumbed down" and there was "a lot less archaeological content and a lot more pratting about".

A special called Brunel's Last Launch, which aired last November, was watched by a disappointing audience of 1.5 million.

"Channel 4 history is all about bringing the past to life in eye-opening, entertaining and innovative ways, from the best archaeological scoops, to big factual dramas," said a Channel 4 spokesperson.

New programmes include a documentary about the hunt for the remains of Richard III – called the King in the Carpark: Richard III – and a new series, the People of Stonehenge.

The final series of Time Team will air next year with a programme looking back at highlights from 250 episodes. There will then be four specials which will play into 2014.