The adaptation of the 2009 book, which was originally illustrated by Quentin Blake, scored 6.34m (27.3%) from 6.30pm to 7.30pm.
Also on BBC One, 4.18m (17.2%) watched Victoria Wood's Joyce Hatto biopic Loving Miss Hatto from 8.30pm-10.30pm. Around the same number 4.18m (20.6%) had watched the Antiques Roadshow for the hour before.
3.61m (20.8%) watched highlights of the last pre-Christmas Premier League games on Match of the Day 2 from 10.30pm to 11.30pm.
Victoria Wood also did well for BBC Two last night, as All The Trimmings entertained 2.16m (9.15%) from 7.30pm to 8.30pm. Her lead-in was The Morecambe & Wise Christmas Show, which had 2.5 million (10.7m).
Over on ITV1, 3.0m (12.8) were caught by The Cube between 8pm and 9pm, with (274k 1.1%) watching an hour later. Joanna Lumley's The Search for Noah's Ark rescued 2.39 million (10.1%) from 9pm to 10.30pm, with an extra 190k (1.0%) floating by on +1.
Ahead of the premiere of tonight's sequel, The Snowman entranced 1.90m (8.3%) on Channel 4 at 6.30pm. An extra 384k (1.7%) watched on +1.
The finale of US drama Homeland scored a similar 1.91m (8.0%) from 9pm to 10.30pm, with an extra 219k (1.1%) tuning in an hour later.
Peep Show, whose current series concludes tonight (December 24), rated 0.58 million (2.9%). A further 164k watched on Channel 4+1 (1.4%)
Channel 5 opted for a movie-heavy evening, with The Family Man winning 1.18m (5.1%) (plus 143k and 0.6% on +1) at 6.45pm, and Bad Santa with 1.3m (6.0%) (plus 158k and 0.9% on +1) at 9pm.
BBC One led primetime on Sunday with a share of 20.5% between 7pm and 11pm, followed by ITV1 on 10%. BBC Two finished in third place with 8.4%, followed by Channel 4 and Channel 5 on 7.9% and 5.5% respectively.
BARB ratings data supplied by Attentional