WA,
It sounds like you may be a victim of the new Tier 4 requirement.
Last year the UK Border Agency introduced new regulations for FTOs which meant that they had to be inspected and audited by the UK's educational authority Ofsted, before becoming what is termed as 'Tier 4' compliant and therefore permitted to continue to act as sponsors for non-EU nationals training in the UK.
Most, but not all FTOs have now complied. I'd check with Bristol GS to see if they have done this yet.
Regards, jez