There are no restrictions on non-sexual nudity being shown on TV during the day. A couple of months ago Channel 4 broadcast a show about art classes at midday, featuring full frontal nudity (both sexes).
And erections can be shown if justified by context, as they can in 18-rated films. It's only porn that requires an 18R, and what's porn is at the subjective judgment of the BBFC.
In any case, Carry on Dick is only a PG so there'd be no requirement to edit it for a daytime showing. Back in the 90s they showed Orlando and Room With A View in the daytime uncut, with full frontals, and they're only PGs.