BBC Antiques Roadshow expert emotional over WWII hero who saved St Paul's Cathedral

Antiques Roadshow specialist Mark Smith had the honour of encountering a descendant of a heroic serviceman who performed an extraordinary act of courage during World War Two.

The beloved BBC show was filming at Stephens House & Gardens in north London this week in a fresh episode that broadcast this Sunday evening (31st August).

Whilst treasure enthusiasts examined items including a golden ring unearthed in an orchard and a legendary photograph from David Bowie's golden era, it was a fascinating wartime artefact that captured Mark's interest.

It's equally the moment that will probably have audiences grabbing for their handkerchiefs, as it features a remarkable deed of valour that guaranteed the famous St Paul's Cathedral remains intact to this day.

Mark presented the objects: "We have on the table a bomb fuse and a George Medal. I have a feeling I know where this story is going to go", reports the Express.

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The specialist then requested an introduction to Ronald Smith, a uniformed gentleman in a monochrome portrait also being displayed, whom the visitor disclosed was uncle to the spouse of one of his relatives.

Ronald enlisted in the Navy at the beginning of the conflict and subsequently volunteered to serve as a Bomb Disposal Officer.

He would eventually receive the George Medal, which Mark characterises as "a very high-up gallantry award. Above it only the Victoria Cross and the George Cross.

"Now, this chap here is actually quite a famous Bomb Disposal Officer," Mark continued, "because this is the man who diffused the German parachute mine at St Paul's Cathedral in April, 1941.

"Without him that day, that landmark that we all know so well, people all over the world know, wouldn't actually, probably, be standing today.

"Now, as with all gallantry medals, there is always a citation. And I have the citation here for Ronnie's day out."

Mark appeared visibly moved as he recounted Ronald's remarkable tale and went on to share the extraordinary account of his courage that secured the survival of one of Britain's most cherished monuments.

"'On the 17th April 1941 an unexploded mine lay in the churchyard of St Paul's Cathedral, about three yards from the cathedral itself'," he began.

"'The mine was completely covered by the parachute, which was impossible to remove. And so, Lieutenant Smith had to crawl underneath and inside the parachute to get at the mine.

"'In this dark and difficult position he commenced to unscrew the disc from the bomb, prior to fitting the gag', which is a device for rendering the fuse inert.

"'Before he was able to fit the gag, a large fire engine was driven past at speed only some 10 yards away. The vibrations sent up by the fire engine started the clockwork mechanism of the bomb fuse.

"'Under the best circumstances, Lieutenant Smith had 17 seconds to make good his escape. But very gallantly continued his operations and was able to insert the gag before the mine exploded.

"'Had the mine exploded, there is no doubt that the main part of the cathedral would have been devastated.' That's incredible."

Mark also revealed he had discovered that when Ronald finally managed to defuse the explosive device, merely two seconds remained on the timer - something he confessed was "terrifying" to imagine.

When the moment arrived for the valuation, the guest was left gobsmacked as Mark disclosed the collection could fetch between £15,000 and £20,000 at auction.

The visitor was nearly lost for words as he exclaimed: "Wow, I never thought it was that much. Wow."

Antiques Roadshow is available to watch on BBC iPlayer.