The "Safe House" used by 'Auntie May' is code-named ISIS long before the Islamic State group adopted the same name.
As hard-right politician "William Sampson," Rupert Graves is very audibly doing an impression of Nick Griffin, who in 2005 was leader of the British National Party.
The logo for the far-right "British Way" party is a not-too-subtle morphing of the British flag into a stylized red swastika with blue and white background.
Sampson's seat of "North Dale Valley" is fictional. No real location is given for the seat, it could include Luton because that's named as the "British Way" election headquarters, but it also implied to include the "East London Council" mentioned.
TV show "Little Britain" is shown on a TV. Anthony Head who was a regular in that series as the "Prime-Minister" appeared in the first series as former MI5 officer Peter Salter.