Called BA exec club on this. Nice lady agreed no way should we accept Jetstar and looked at alternatives for us with CX and MH in J. No joy as we are quite tight on the date(s) due wedding in PER.
Solution was canx and get everything back and source alternative.
Indeed though seems awful that it can be determined that such a re-booking is considered a like for like...incredible really.
thanks for some of the suggestions...will take time and also keep eyes peeled for perhaps AVIOS use opportunity...plenty of time....