In the past I have found the presidents club folks in terminal E to be wonderful. Earlier this year I was scheduled to fly IAH-EWR-BRS when there was a ton of delays at EWR due to a storm. They delayed all flights from IAH to EWR until it cleared. There was a good change I would miss my EWR-BRS flight. The BF concierge re-booked me on the IAH-LGW direct flight, I got the last BF seat. They were wonderful.

There are a ton of options to get you over to the UK in time. You are right that getting there early is your best way of keeping your options open, including the ones through EWR.