Antiques Roadshow guest says 'I'm astonished' as special WWII item from 'secret army' with links to Winston Churchill receives staggering valuation as expert Robert Tilney says it has 'totally made my day'

An Antiques Roadshow guest was left 'astonished' after receiving a staggering valuation for his World War II 'fighting knife'.

Expert Robert Tilney said the 'wonderful, wonderful thing' had 'totally made my day' as it is one of only 'a few thousand'.

The knife was used by the guest's father when he worked for the Special Operations Executive (SOE), also known as 'Churchill's Secret Army'.

It was explained that the hand-made Fairbairn–Sykes fighting knife was bought in order for Lieutenant L.H. Massey to complete commando training for the force and then train the Polish resistance the same way.

The blade was a pass for the 'Inter-Services Research Bureau' (ISRB) - a fake organisation based in Baker Street as a front for the SOE. 

An Antiques Roadshow guest (seen) was left 'astonished' after receiving a staggering valuation for his father's World War II fighting knife

The Fairbairn–Sykes fighting knife was made specifically for close combat for secret commandos operating in occupied Europe, by creators William Fairbairn and Eric Sykes

Expert Robert Tilney said the 'wonderful, wonderful thing' had 'totally made my day' as one of only 'a few thousand' before giving it a £5,000 valuation

'This is interesting,' Mr Tilney began, 'this is a pass for Lt. L.H. Massey of the Inter-Services Research Bureau.

'It's interesting because the Inter-Services Research Bureau didn't exist.'

The guest explained that after being invited to join the ISRB, his father was taken to another room and told the true nature of his employment by senior officers.

'When my father was told to report to the headquarters of the ISRB in Baker Street, London, he was given this pass and told he'd joined the organisation but not what it was or what it did,' he revealed.

The ISRB was the SOE's cover name, not that Lt. Massey had heard of that either.

One of the new recruit's first tasks was to get his own kit, including a 16 shilling fighting knife from Wilkinson Sword. 

The FS fighting knife was developed by William Fairbairn and Eric Sykes specifically with the hand-to-hand combat which would be carried out by the SOE, in which the latter worked with Lt. Massey.

That meant that the dagger brought on the BBC One show had been handled by its very designer, leading Mr Tilney to say: 'With that, I would put £5,000 on that.

'It's the most amazing thing - handled by the guy who invented it. That has absolutely made my day.'

The guest's jaw dropped as he said: 'I'm astonished.'

The guest's father, Lieutenant L.H. Massey, had to buy the knife before going for commando training in the Scottish highlands

Lt. Massey's dagger was purchased for 16 shillings from Wilkinson Sword

Churchill's SOE was formed in 1940 to conduct espionage, sabotage and reconnaissance on the occupied continent, as well as to aid European resistance movements.

Fairbairn and Sykes taught agents who were destined to serve in the field in Arisaig, Scotland, though the main base for the SOE was in Baker Street.

Agents also undertook parachute, demolition and security and 'tradecraft' training.  

It was dissolved after the war in 1946 by new Prime Minister Clement Atlee despite the SOE's chief, Lord Selborne, advocating for its continuation despite having created a tense relationship with other governmental and military bodies.