I'm not familiar with the UK price rises, but I can tell you that this will have no effect in the amount of IRC's you send to someone.
Regardless of how much an IRC costs, you can exchange it in another country for the minimum amount of postage an unregistered, standard letter by air mail can be sent overseas. So, even if the price of postage rises in another country, the IRC should still do the same job. You won't need to add any extra IRC's to your postage, 2 will be sufficient.
However, the rise in postage costs will have an effect. This will probably mean that the cost to send your request to another country will rise, by how much, that I don't know. You'll have to find that out (see Ian's sticky at
http://www.fanmail.biz/mboard/viewtopic.php?t=14167.)
Good luck tinker_mel!
nowandagain [rockon]