Thomson have updated their Dreamliner blog this morning to announce that 787 longhaul flights will start on the 8th July to Cancun and Florida. They don't mention UK origin airports, so I assume that they will all start on that date, and will have at least 2 aircraft in service. No mention of any warm-up short haul flying prior to that. Latest All Things 787 blog update last Friday hypothesised that Thomson's deliveries would start in June - I assume it would need to be early that month to allow the necessary training and short haul flights (if still planned) to happen.