I think - you may want to check - buy the UK's quarantine is 30 days ?? do check. that would not be worth the cats' trip over there plus more trauma. If you could take the cat right off the plane, then I'd do that.
I've not traveled for years b/c of my pets.
I finally found a great boarding place now but am still leery about leaving them.
IMHO, cats can do a little better w/out human contact & a sitter coming over a few X's daily would be OK -