You can look up the info on NHS pay rates by going to their website and having a look at the agenda for change booklet. Lists all the pay bands in the NHS and gives the rates. A physio typically starts at Band 5 and that would equate from memory to about £20,600 per year with an outer London weighting of about an extra £2k and an inner London weighting of about £4k. So, central London new physio would be on about £24k. Not ££££'s as suggested above, but not bad.
Privately, well it would depend on client base and where you work. I saw a specialist a while back who charged £100 an hour and was booked solid for the three days a week he worked. So, for guys like him I'm sure you are looking at in excess of £100k a year, but this isn't the norm. You will usually pay around £40 for a 45 or 60 min appointment with a private physio, so if you multiply this by 6 (account for a lunchbreak and not being completely booked every day) that gives £240 a day, approx £1250 a week, call it £5k a month which would be £60k a year. However, take out of that tax, hiring a room, paying for things like massage oils, maybe a receptionist etc etc, it probably whittles it down quite significantly.
My mate who is a senior physio (band 6) does both. Works a 9-5 as a neuro specialist in the NHS and then does private clinic work on evenings and weekends when needed. There is a big cross over now between private and NHS in that you can be referred to a private clinic on the NHS (I believe), so its become much more flexible.
Maybe someone like Jackie will be along shortly to give a more definitive answer.