I did the LPA for my late mother in law and for my Mum. It is dead easy to do yourself if you sit and take your time. It took me about 3 hours to do both forms. A LPA can be set up at any time, but as long as your Mum is 'OK', it can just sit there gathering dust. If something happened to her (lets say a stroke...heaven forbid) you have got the LPA and can immediately sort things out for her. If you waited until the day after the stroke, you could be waiting 10 weeks to be able to handle your Mums affairs. There is actually a good argument that everyone should have an LPA 'just in case'.
On the link on murraymints post, contact the Office of the Public Guardian and ask for the froms for LPA for 'Health and Welfare' and 'Property and Finance'. Do them both...its cheaper and they are nearly identical forms. I found it was easier to do real forms than filling it all in on line. The OPG send an excellent how to do it booklet and it is much easier to understand with all the forms in front of you. You can have as many attorneys as you like (we had 5 for my mother in law)...its the same price. You just need to download an extra sheet for each person. They all have equal standing, but you can put a proviso in about who is number 1 etc. You will need an independant witness to witness signatures and a 'person to be told'. This is usually a friend of your Mum who is told what is going on. This is a safeguard so that they can blow the whistle on you if they think you are trying to nick all your Mums money or something.
Send the forms off and about a month later they should all come back stamped and registered. Thats it. One extra thing, if you Mum is on any sort of government benefit (except for state pension I think) she can have it for free...form included in the pack. Good luck!