I've used a Nikko Sterling for years on various air rifles including a .22 Diana model 52. If any air rifle will test a scope well it'll be a 52! It lased fairly well but started to have issuess last year so, after much research and head scratching I stumped up and bought a Hawke sidewinder 10x44 (I think it was). Fixed mag works for me and keeps the weight down. Also easier for knowing your range markers and aim off points. Anyway, the build quality was awful and the sight picture terrible so it went back. I know a lot of people love them and have no problems, maybe mine was a 'Friday afternoon' scope, who knows? I now have an MTC Viper 10x44 side paralax, and it is awesome! Great quality, great glass, sturdy build. Top stuff and worth the extra spends. Both of these scopes are about double your £100 though, so sorry if that's not helpful! Second hand bargains can be found though.
It's worth buying the best mounts you can too. Sportsmatch have always done well for me. Make sure they've got 2 screws per side (4 in total) to hold the top clamp down, and 2 screws in in each rail clamp. Single screw clamps are useless. If there's a rail stop screw, use that too. Even if your rail isn't holed for one it'll still bite down (although may mark the top of the rail) and provide some stability. The fieldsports channel on YouTube have a decent vid on scope clamp set up, worth a watch.
James