I suspect that you may be asking the wrong question.
The problem, if it exists, is not to do with charter .v. scheduled. If it exists it is more likely to be with state of registry.
A charter or budget airline with aircraft registered in the UK is required to meet the same safety standards as BA, Virgin or anybody else here. If they are cutting costs, it's going to be on admin, salaries, catering, cleaning, etc. - safety isn't optional.
CAA announced the banning of a number of foreign airlines from flying into UK airspace last week, it's noticeable that none of them are using aircraft registered in the UK, or for that matter the US or any European country where the safety standards are broadly similar.
G