Costs without proceedings

If a claimant makes a CPR Pt 36 offer before the issue of proceedings and that offer is accepted, is the claimant entitled to his costs? It is clear that he would be if proceedings had been issued, but Pt 36 makes no comment on the costs effect of a pre-issue offer being accepted. Alternatively, if a claimant were to make a pre-issue Pt 36 offer and included a provision that acceptance was conditional on payment of the claimant’s costs would that be a valid offer for the purposes of Pt 36 or not? As a substantial amount of work is often needed to prepare a claimant Pt 36 offer it would seem fair, and in the spirit of avoiding unnecessary proceedings, if costs could be recovered pre-issue. If they cannot, one would be better off issuing and then making a Pt 36 offer immediately thereafter?

As a matter of vires, the CPR only apply to proceedings which have by definition