In Digbeth, central Birmingham, a hail storm and rain failed to dampen the celebrations.
There have also been celebrations in Belfast, Dublin, Londonderry, Armagh, Newry, Enniskillen, Downpatrick and Edinburgh. Manchester staged its events last weekend.
The Mayor of London’s office organises the festival in the capital to bring the “best of Irish culture and a packed programme of great entertainment to Trafalgar Square”.
Marching bands and dancers made their way from Piccadilly.
An official St Patrick’s Day event has been held in London since 2002.
The Birmingham parade has been running from Digbeth since 1996.
In Birmingham, a full day of music, dance and activities was planned at various venues.
“Throughout the years we have been subjected to all weathers, getting sunburn one year and coming close to frostbite the next,” said Gerry Jones from Off Our Trolly Arts, which is part of the festival.
“I hope in some way we have made a difference to add colour and spectacle, to create wonderful memories for both the children taking part, and the tens of thousands of people who attend the event.”