It would be difficult for them to do that because the vast majority of the European zero hour crews don't have the right to work in the UK. I presume you're referring to Buzz crew because the only other zero hour pilots are contractors (fixed and floaters), and they are not cheap for the company.
Also, the buzz crews aren't able to operate the G or EI reg aircraft whilst simultaneously operating SP reg. There's a sim between each time they transfer reg. The floating guys can operate EI reg but again, they are very expensive and recently got a payrise so it won't serve the alleged intended purpose.