As Carlton points out D19 must provide some considerable comfort.
What will be of interest to HMRC in practice is whether the paperwork is in order. Basically, can they find enough nails in the coffin to levy CGT only on H. The bigger the numbers the greater HMRC's interest.
For example, is there any evidence to suggest that W is acting as nominee for H. Other things being equal, the less W has been involved prior to exchange the stronger the possible argument W was merely as a nominee.
Has the (presumed) declaration of trust been timely and correctly executed. Did W file a Form A restriction.
50% (or the relevant percentage) of the net proceeds of sale should be remitted directly to the bank account of each of H and W ie not to their joint account.
Just a few thoughts.