Green’s Dictionary of Slang

heavy mob n.

also heavy squad
[heavy adj. (4b)]
(UK Und.)

1. a gang of thugs.

[UK]B. Hill Boss of Britain’s Underworld 7: I had my own mob, probably the toughest team of screwsmen ever [...] We were called the heavy Mob.
[UK]G.F. Newman You Flash Bastard 20: The straight businessmen, abetted by the front men like Peter Rosi, had been moving into and dominating areas where firms and heavy mobs once operated almost exclusively by violence.
[UK] in G. Tremlett Little Legs 125: Telling people that he was with the ‘heavy mob’ now.
[UK]J.J. Connolly Layer Cake 265: That’ll lead to a shitload of complications. Their heavy mob’ll come after us.

2. physically tough police or prison officers used in violent situations.

[UK]J. Phelan Tramp at Anchor 167: If the convict were not completely acquiescent the ‘heavy squad’ gave him a tanning.
[UK]‘Charles Raven’ Und. Nights 98: Rex shouted: ‘Scarper blokes, it’s the Heavy Mob’.
[UK]F. Norman in Police and the Public in Norman’s London (1969) 129: He was a big geezer and was obviously a member of the heavy mob.
[UK]J. McClure Spike Island (1981) 384: There’s no doubt we were the heavy mob, we were the snatch crowd.
[UK]J.J. Connolly Layer Cake 148: He’d get a serious beating from the mufti, the heavy mob.
[UK]N. ‘Razor’ Smith Raiders 27: Bob and Terry were trying to ward off truncheon blows from the hastily assembled heavy mob.

3. (also heavies) officers from the Flying Squad and, formerly, the Special Patrol Group; thus heavy, the car they drive (see cit. 1989).

[UK]‘Charles Raven’ Und. Nights 194: In steamed the Law, not the local bogies neither but the Heavy Mob, the genuine Flying Squad.
[UK]P. Beveridge Inside the C.I.D. 42: In January, 1940, I was promoted to Chief Inspector and given charge of the Flying Squad [...] or the ‘Heavy Mob’ as it is called by the criminal fraternity.
[UK] ‘Screwsman’s Lament’ in Encounter n.d. in Norman Norman’s London (1969) 67: We cruised along at a steady ninety, this drag a lovely job, / With Drummer Bill behind the wheel, we’d outstrip the heavy mob.
[UK](con. 1920s) J. Sparks Burglar to the Nobility 27: After me and Gerogie had stolen the famous Wernher Collection of jewellery [...] the Heavy Mob had taken to following Georgie around .
[UK]D. Powis Signs of Crime 187: Heavies Police officers from either the Flying Squad or the Special Patrol Group.
[UK]J. Morton Lowspeak 72: Heavy [...] a Flying Squad car, usually used in the plural.