Don't forget you'll need another £150 approx for a stirrup pump or bottle.
As for which rifle, go and handle different ones at your local RFD and get a feel for them. The more "right" it feels when shouldering it the better you will shoot and the more you will enjoy it.
The ultra is a good rifle and is nice and compact, try and go for the SE multishot if you go this route. The Hatsan is heavier but still a good rifle, check the serial number as the first 4 numbers are the month and year of manufacture. The early ones had a few issues. Walther have recently introduced the Rotex R8 in .1