According to my copy of the Central Bus Timetable for 1967 the following services ran on Christmas Day:
2B Golders Green - Crystal Palace
5B Aldgate - Becontree Heath
6 Kensal Rise - Hackney Wick
8 Willesden - Old Ford
9 Mortlake - Hammersmith(Brook Green Hotel)
11 Shepherds Bush - Liverpool Street
12 Oxford Circus - South Croydon
14 Hornsey Rise - Putney
15 East Acton (Goldsmiths Arms) - East Ham
16 Cricklewood - Victoria
17 East Finchley Station - Farringdon Street
18 Sudbury - Paddington Green
19 Finsbury Park - Clapham Junction
24 Hampstead Heath - Pimlico
25 Aldgate - Becontree Heath
27 Turnham Green - Archway
29 Palmers Green- Victoria
30 Roehampton - South Kensington
31 Camden Town - Chelsea
35 Chingford Hatch - Brixton
36B Victoria - Grove Park
37 Peckham - Putney
38A Victoria - Hackney (Clarence Road)
41 Archway - Tottenham Hale
44 Vauxhall - Wandsworth
47 Stamford Hill - Lewisham
52 Willesden - Victoria
53 Plumstead Common - Elephant and Castle
58 Walthamstow (Crooked Billet) - Canning Town
59 Charing Cross - South Croydon
68 Aldwych - South Croydon
73 Stoke Newington - Hammersmith (Tottenham allocation)
73 Hammersmith (Brook Green Hotel) - Twickenham Station (Mortlake allocation) N.B. Route operates in two separate sections.
77C Aldwych - Clapham Junction
88 Shepherds Bush - Mitcham
95 Elephant and Castle - Tooting Broadway
101 Wanstead - North Woolwich
104 North Finchley - Moorgate
123 Manor House - Walthamstow (Beacontree Avenue)
127 Waltham Cross - Mornington Crescent
130 West Croydon - New Addington(Homestead Way)
134 Friern Barnet - Archway
141 Wood Green - Moorgate
141A Elephant and Castle - Catford (St. Laurence Church)
142 Edgware - Kilburn Park
144 Turnpike Lane Station - Edmonton (Cambridge)
149 Ponders End Garage - Liverpool Street
171A Peckham - Abbey Wood
184 Elephant and Castle - Brockley Station
185 Victoria - Forest Hill
207 Southall (Delamere Road) - Shepherds Bush Green
208 Clapton Pond - Bromley - By - Bow
210 Golders Green - Finsbury Park
212 Muswell Hill - Finsbury Park
220 Shepherds Bush - Tooting Station
249A Chingford Mount - Victoria and Albert Docks
253 Finsbury Park - Aldgate
262 Leyton (Bakers Arms) - Stratford
266 Colindale (Annesley Avenue) - Hammersmith
269 Enfield Town - Turnpike Lane Station
277 Hackney Station - Cubitt Town
Buses started running from after 8am, e.g the first 2B left Stockwell Garage at 08.06 heading for Victoria, but some routes didn't start running till nearer 9am. As you stated all buses were back in their garages by 16.00. Oh for a similar service on Christmas Day now!