I believe BBC instigates line 23 switching for widescreen flagging within the BBC and sometimes this gets passed on to the regional transmitters. It's a problem that they are aware of. It only effects BBC1 from some regions. Consequently you may find watching BBC1 via the RF output of a digibox you get widescreen switching too (as per channel 4 terrestrially).
EDIT: ...and of course your VCR is probably recording the wss flag from BBC 1.