The all-action owner of Holkham Hall is preparing to race against two of his senior staff – and 150 other hardy competitors – in a gruelling four-event coastal quadrathlon.

Viscount Coke is training for the Norfolk Superhero Challenge on June 18, which involves swimming, kayaking, cycling and running through some of north Norfolk's finest scenery, including his own family's estate near Wells.

He will be up against estates director David Horton-Fawkes and estate surveyor James Bracey in the charity event which, in its fifth year, will be raising money for Wells Hospital's Mermaid Appeal.

Despite working so closely together, the three men all signed up independently for the race – only realising later the opportunity from some friendly estate rivalry.

Lord Coke said: 'I think it is something of a mid-life crisis for most of us. It is not supposed to be competitive, but of course we are all secretly being competitive about it. I think we're all very worried about the swimming, but I have now proven that I can at least go one mile without drowning.

'I think it would be wonderful if all three Holkham people arrived at the finish line together, arm in arm. One or two of us might need carrying, though.'

The race begins with a one-mile coastal swim and four-mile kayak through the creeks at Burnham Overy Staithe before a 38-mile cycle course returns through the Holkham Estate to Burnham Overy. Finally, the racers face a seven-mile run across sand, tracks and marshes – with the last mile an energy-sapping slog through the mud flats.

Competitors race in pairs, with the fastest teams expected to finish in just over four hours.

Lord Coke, now fully recovered from breaking his collar bone while mountain-biking in the Swiss Alps last year, will compete alongside his team-mate, the Rt Hon Hugh Crossley from Somerleyton Hall near Lowestoft.

Mr Horton-Fawkes, who at 47 is two years older than Lord Coke, said: 'I am the oldest, so I have every excuse for coming last. Of course it is competitive, but it is more about the fun of it.

'My partner, Harry Cory Wright, has done this two or three times before. He asked me if I wanted to do it an, stupidly, I said yes before I realised what was involved.

'I suspect Tom Coke could be a dark horse – he is able to train while we're all working!'

Mr Bracey hopes to raise �5,000 for the Wells Hospital appeal to buy renal dialysis equipment.

'It is a really good local charity and there's a lot of support for it,' he said. 'I used to be in the army and I have done a few marathons, but that was 10 years ago.

'Physically, it'll be really tough. The first two events are mostly using the arms and then you are using a completely different set of muscles for the cycle and the run. '

For more information, visit www.norfolksuperhero.co.uk.