Hi,
HMRC’s guidance on reclaiming VAT on pre-registration expenses is here: https://www.gov.uk/vat-registration/purchases-made-before-registration
Provided that the criteria are met, the reclaimable VAT is the amount shown on the suppliers’ VAT invoices, and should be claimed in box 4 of the VAT return. I can’t see why Corporation Tax would restrict any ability to claim VAT.
I have no involvement in Corporation Tax though, so don’t know what impact any retrospectively reclaimed VAT may have on CT returns. It might be that the VAT claimed would be regarded as a reduction in expenses for the year in which it was claimed? But you’d need someone with CT knowledge to confirm.