security guard is not one of the occupations prevented by BR
however some of your potential jobs may be sensitive so the employer could object. although an employer cant turn you down for selection to a job for being BR, in a competitive market they may find "a more suitable candidiate"
On a practical note, if time permits obtain your licence and job, then if you are able to negotiate a settlement with your creditors do so, if not apply for BR but in view of your job inform your employer, if they have seen that you are a good reliable worker thay are likely to keep you on.
Richard is right. I have recently dealt with a debtor who held a security licence. I checked with both The Isolvency Service and the SIA, both of whom confirmed that bankruptcy did not affect your security licence.