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.
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There will be a few showers in the north, but otherwise dry for many with warm sunny spells before heavier rain in the south west.
David Davis is hoping to push Brexit withdrawal talks towards discussions on a future trading relationship between the UK and EU.
A fine start to Sunday but rain moves in from the southwest later on.