Spoke to my MW and consultant and they both said the same.
They said many women have are positive for strep B and that it's never a problem. That just because you come up positive on the tests doesn't mean it's going to flare up, may just lie dormant and that the only vulnerable babies are at risk. They say out of every 10 women that are positive for strep B only about 1 of them will have any issues.
That's why they don't offer it and don't like to do it as they'd be giving unnecessary AB's to mothers (and babies) during birth that could cause more issues.
Hence we decided against it.