hey
@Ben1989 just to give you an example of what happened for me and my spouse --
we flew from heathrow to boston in late april. my spouse had applied for an ESTA online and it was approved in a couple of hours; at the airport though, we (and, it appeared, everyone else on the flight who was an american married to a non-american) were put to the side and had to talk to a representative from the USA and provide our marriage certificate before we could complete check in. this took nearly an hour, and that was at noon.
I'd definitely make sure you have time built in for the american questioning etc at the airport, presumably in manchester if that's where you check your bags for the entirety of the trip. on the other hand, i wouldn't be surprised if entry requirements to the usa change in the next few weeks, so it might get easier.