Or, as Wikipedia puts it
'The scene where Elton says he and Ursula have 'a bit of a love life' was criticised by some commentators, who felt that the resultant implication of having oral sex with a paving slab was unsuitable for Doctor Who's large audience of children; others, however, dismissed this dialogue as a harmless joke that children would not understand.'
( ,
Tue 12 Feb 2013, 15:13,
archived)