I bought a sterling draft from An Post (GPO Dublin) last year - paid for it in cash over the counter (they didn't accept laser/debit cards for drafts at the time, don't know if it has changed now).
Suspect that there is a materiality clause to this from the point of view of money laundering. I can't see AnPost issuing a GBP draft for e.g. 10k and taking 11k odd in Euro Cash for it. Probably okay for a GBP100 draft though.