Demonstrators chanted "how many cops in the BNP"? As membership of groups like the BNP and fellow Fascists the NF and Combat 18 etc, is forbidden by the police contract of employment, the honest answer is probably not many, but that doesn't stop some police being Fascist sympathisers...
In April 1979 for instance anti-fascist protestor Blair Peach was beaten to death by officers of the Metropolitan Police's brutal Special Patrol Group (SPG) - the same unit now known as the Territorial Support Group (TSG), during a protest against the NF in Southall. After Blair Peach's murder a team of detectives headed by Met Police Commander John Cass conducted an internal investigation, raiding Police lockers in the SPG HQ - they retrieved a small arsenal of illegal weapons, including several knives, two crowbars, a whip, a 3ft wooden stave, a lead-weighted leather stick and various illegal truncheons, one SPG officer was discovered attempting to hide a metal cosh and another SPG officer was discovered hiding a cache of Nazi regalia.
More recently, over Xmas 2008, the Post Office intercepted a parcel containing a Taser stun gun. Police raided the home of the parcel's intended recipient Ellis Hammond, and found 8 combat knives, 4 BB guns, a CS gas canister, knuckle duster, telescopic truncheon, crossbow, replica AK47 assault rifle, BNP literature and Nazi DVDs, Nazi T-shirts and Ellis Hammond's BNP membership card (his membership was also confirmed by the leaked BNP members list). Ellis Hammond was a serving Metropolitan Police Community Support Officer, and, for anyone who thinks this was an isolated incident, although the Police deny this, the Daily Mirror say Hammond's Police colleagues covered-up for this dangerous Nazi, withholding information about his Police work from the prosecuting Magistrate and from the Crown Prosecution Service. Predictably Ellis Hammond was "allowed to resign from the Met Police and did not face a disciplinary hearing" and "was left off with a conditional discharge".
On the 9th March 2013 former English Defence League demo steward Bryan Powell & Welsh Defence League & Casuals United organiser Luke Pippen, organised an openly Nazi "White Pride" rally on behalf of South Wales NF in Swansea, drawing a small crowd of hard-core Nazis from all over Britain. The Nazis flew flags of the NF and of violent race-hate groups like Blood & Honour, yet South Wales (Heddlu) Police officer (collar number) 3896 was evidently willing to have his photo taken (possibly by Bryan Powell), posing with ex-EDL activist and Nazi Wayne Baldwin (see photos). For anyone who thinks this might have resulted from an innocent misunderstanding, Wayne Baldwin was already well-known to South Wales Police from national media coverage of EDL & WDL demos, and even if officers hadn't been properly briefed about the "White Pride" demo, Baldwin's "deaths-head" SS t-shirt & Swastika badges were still a bit of a give-away!