Your solicitor should be able to obtain the indemnity for you, but if not you could try ChancelCheck - they carry out the searches and also arrange insurance.
my solicitor organised this. One thing to watch out for - the basic policy applies only to you and your current lender (if you have a mortgage) so if you move then the new owner would have to repurchase and if you move mortgage lender then you would need a new policy too. You can 'upgrade' to a policy that covers the building. All a bit of a racket as my mum would say!