232 Typhoons to give a force of 137 in-use aircraft (seven x 16 Unit Establishment front line squadrons; the OCU; the OEU plus a couple of trials aircraft). Remaining 95 airframes to be rotated in and out of use/replace lost airframes over the course of the projected minimumprojected 30 years of service.
AIUI, 150 x JCA figure originally included the notion that some of these aircraft might replace some GR4s. There is a requirement for about 60 in use JCA at Lossiemouth, I believe, with the balance being the attrition reserve/means of evening out the FI across the 30+ year service life for the type.
If JCA replaces some GR4s, it'll be as the FCAC(Future Combat Aircraft Capability, IIRC) in two x 8 aircraft (yes, that's right, eight, not 12...) squadrons, but that's not been decided. JCA OEU will be in the US and consist of two aircraft.