Police were heard to tell anti-Thatcher protesters in Trafalgar Square that Millwall football fans had joined the demonstration and were "throwing bottles of urine" at officers.
Millwall supporters were earlier involved in crowd trouble during the club's FA Cup semi-final against Wigan at Wembley.
More top news
Mild evening rounds off October ahead of cooler temperatures over the weekend.
Two families who lost men in military campaigns almost a century apart have made an emotional visit to the Tower of London's sea of poppies.
A British jihadi who has lost two of his brothers in Syria has told ITV News that he intends to stay and fight until he is also killed.