@craigtdannUnfortunately just been sent around circles and had both the share broker (transferor) and IG (transferee) both saying CREST numbers can't be provided, IG says the other broker has to get in touch, the broker says IG needs to give me the CREST number as I am the account holder.
This is just very frustrating and disappointing hence, I've had to go ahead with the existing broker instead of transferring to IG which is such a shame.