I will have to double check injector durations but we've tried another ECU and the fault remains. I will recheck fuel trims etc next week but the ECU is seeing full throttle and there is no MAF fitted.
This engine only uses a MAP sensor and this is seeing atmospheric pressure with the throttle wide open.

I agree that the vacuum does seem a little low and that's why I checked the cam timing, exhaust back pressure etc. I've even removed the cam wheel to make sure it hadn't sheared the woodruff key but all is well.