Hi BooBoo,
As BAHumbug just said, the BA LHR-BCN will be in T1 then T3 per;
http://www.terminal5.ba.com/media/en/BA_T5_moves.pdf
If on one ticket then BA/VS should interline the bags but if on two tickets they will probably not interline and you will need to collect the bags and check in again
Regards
TBS