The other factor now is the ZEV mandate. Manufacturers, and thus dealers, need to ensure 22% of their vehicles sold in the UK this year have an EV certificate credit. They can get a certificate by selling an EV, borrowing against a future year, buying certificates from other manufacturers (e.g. Tesla)… or earn partial credits by reducing their fleet emissions (as it’s the government, there’s of course a complex formula to work that out). This latter point helps PHEVs as their emissions are a quarter or less of a typical car now - so more incentives to sell PHEVs can be expected, just as manufacturers (including Lexus) are now offering ridiculous discounts on new EVs.
Every certificate (car) short of the 22% will cost the manufacturer £15k per vehicle - so there’s big money on the line. Much better to e.g. give a £8k PCP deposit contribution (as Honda have for their EV) or other discounts on PHEVs, than pay a £15k penalty later!