May look difficult, but no problem to do in the head - £1 19/8 1/2p.
Now the equivalent in decimals would actually be quite a bit harder to do in the head.
Once the pennies and the shillings and so forth were gone what's the point in hanging on to the pound? I'd have not the least problem in going over to the euro, which is worth just about one pound already anyway.
Just do it - and declare that the existing coinage is still valid, with one pound being equivalent to one euro, and one penny equivalent to one cent. Oh, and declare that from now on the name for the unit of currency will be that good old Latin word "Quid"