A family were given an impromptu tour of Number 10 after they bumped into John Prescott in Whitehall.
Mr Patel said the deputy prime minister stayed off politics
The Patel family were invited in to the famous address after they got chatting to the deputy prime minister, who is standing in for holidaying Tony Blair.
Pinakin and Premila Patel, of Harrow, north west London, were looking at a new war memorial to women with their daughters when Mr Prescott approached.
IT consultant Mr Patel said Mr Prescott was a good guide who "knew his stuff".
The deputy prime minister had abandoned his Jaguar, after a meeting with ministerial colleagues, in favour of a stroll in the August sunshine.
He struck up a conversation with the family as they looked at the memorial to women who had contributed to the war effort.
Then, to their surprise, he asked if they fancied taking a look inside the seat of power.
Mr Patel said: "I was totally taken aback - I thought he was joking at first, and then I thought maybe he only meant the kids, but it was all of us.
"It was a really pleasant surprise and they loved it, it was certainly a good holiday highlight.
"I don't think they realise the importance of what takes place there but they will in the future and they'll remember it forever."
He continued: "It was more for the kids, it was more on their level.
"It was almost like a private tour. He knows his stuff.
"They thought he was a very nice man, but I don't think they understood that he is the main guy in the absence of Tony Blair."
Once inside, the family got to see the Cabinet Room, the White Room, which is often the setting for interviews, and the Grand Staircase with portraits of Britain's previous prime ministers.
The Patel family were on a sight-seeing trip to central London
After a 15-minute private tour, the Patels were then escorted out by Mr Prescott.
When asked for his personal assessment of Mr Prescott, the 38-year-old father of three said: "For the day he was great."
It is not the first time the deputy prime minister has treated families to unexpected tours of the corridors of power.
His spokesman said he had previously shown families around his own historic offices, the Commons and Downing Street.