FORMER Hardye's School pupils were astonished when they turned on their TV sets and spotted their old teacher - still in his mortar board and gown.

Andrew MacTavish, 66, who taught at the Dorchester boys' school until 1976, was on the small screen hectoring pupils on their standards of behaviour, with a grim glint in his eye.

But this was not their past coming back to haunt them, but a one-off experiment for Channel 4 to send modern pupils back to school in the 1950s, called That'll Teach 'Em.

Mr MacTavish, who was involved with the Combined Cadet Force (CCF) in his time at the Dorchester school, is still filming the series, which throws today's teenagers into scratchy uniforms and sees them eating spam fritters and spotted dick, as well as taking exams of the era.

He is seen tearing into pupils who misbehave in the programme, which is aimed at giving pupils a genuine experience of education in the 50s - but pupils and masters who knew him when he taught at Hardye's say they remember him as a kind and caring man and the man who with a group of boys discovered Portland's Blacknor Caves.

Mike Bowman, who was head of art at the time, said: "I couldn't believe that was him on the box!

"He always was larger than life - he was in the Cambridge Footlights with John Cleese - and in the programme he's being a proper martinet, but he is actually extremely kind, witty and caring and an amazing all-rounder."

Dave Bowen, who took over from Mr MacTavish as head of English, said: "I remember when he came flying across the cricket field to interview me on his bike, dressed in his gown, and conducted the interview in the CCF hut."

Farmer Peter Stockley, 48, remembers borrowing Mr MacTavish's oversized helmet for a rock climbing expedition - one of the few times he remembers safety measures being used.

He said: "We all got on all right with him - the CCF was a big boys' club and I loved it. Everybody is so scared of doing anything now, but we would abseil without a safety rope and no helmets, apart from when I borrowed Mr MacTavish's.

"Another time we went camping in Snowdonia and woke up floating on our lilos after a blizzard. Some boys didn't have lilos and were soaked through. We had to wrap them in foil until help arrived."

Daud Rashid, who was also in the CCF while Mr MacTavish taught at the school and has since moved to the Netherlands, said: "I'm sorry to have missed the programme.

"Mind you, judging by the number of British shows on Dutch TV I'm sure it won't be long before we see it here complete with Dutch subtitles!

"As one of my many good teachers at Hardye's it's nice to think of Mr MacTavish achieving national fame. I certainly associate him with the good old days; a period when teachers had authority and commanded respect but gave real commitment, care and guidance. I hope that Mr MacTavish can help to highlight the failings of the current school system and to bring about change for the better."

Mr MacTavish, speaking to the Echo, said that he has "very fond memories" of his time in Dorchester and added that it was one of the most exciting times of his life when he and the cadets discovered Portland's longest network of tunnels, the Blacknor Caves.

He said: "I don't think I could have done it with any other group of boys.

"A boy called Dave Churcher, an excellent caver, abseiled down the 100ft vertical drop of Blacknor Cliff after we saw what looked like an entrance halfway up. Two boys, Churchill and Avery, went down the tunnels and did a preliminary survey, but we came to a blockage, with a tiny hole that we couldn't get through.

"But the smallest boy, Paul Grassby, appeared on the other side, saying, 'you can get through!'

"Hardye's was a happy school when I was there. There was no pressure to go to university, because we wanted the boys to do what they wanted in life.

"There was one particular boy, called Old, who did very well, but didn't want to go on to further education but went into thatching and was very happy. I'd love to hear from him again."