The only mod I had when I went to BBR for a stage 1 was a Corksport SRI & TIP (claimed 20-25 bhp increase) but needed uprated fuel pump internals after the map. This could well be the problem the Bristol chap had at Litchfield ?
Neil McKay @ BBR took it for a test run after the map and showed me the logs with dropping fuel pressure, so fitted high flow internals and retested - all OK

Car hasn't missed a beat in the 10 months since being mapped.
I've had the Corksport turbo back exhaust fitted recently and the turbo response is noticeably quicker (and bloomin loud at the tailpipes

), so I'm keen to see what it produces at the Powerstation meet in March.