I frequently have a long layover in LHR while waiting for my ROI flights - I think the last time was 5 hours - and as Tinkerbelle has said Revivals is a perfectly acceptable place to wait. It's no Clubhouse as it is small with loads of shower rooms and a small dining area. It's perfect for a shower and breakfast and possibly a treatment. There are newspapers and magazines as well as some PCs if you haven't your laptop with you to help pass the time.
The difference between the CH and Revivals is the rapid turnover of clientele. Most people are in there for a shower and breakfast before leaving with a few hardy souls who have onward flights left behind. There is a lull between the early morning arrivals and the mid-morning bank of flights and it can be quite eerie to be the only ones there as they start setting up the tables in preparation for them.
The important thing to remember is that if your bags are checked all the way through to Belfast you have to exit through security to get to Revivals and not use Flight Connections since Revivals is landside
