Take a look at this list of locks
Best locks
I have a
Kryptonite New York Fahgettaboudit Mini and I find it perfect for my needs..... after I fit it around seatstays, wheel and post there is no room for a mini bottle jack and you cannot cut an 18mm thick shackle with a boltcropper, not even a 42" cropper. Having said all that, if a thief really wants your bike then he can use a power tool and that can cut the lock in a little over 3 minutes.
I also have a
Kryptonite Evolution Mini Lock a little smaller that the other one but it fits perfectly around the seattube, wheel and post.
I use
Evolution Mini lock if I need to leave my bike for 15 minutes or less. I use the
Fahgettaboudit Mini lock for anything longer, however, if I need to leave the bike on a quiet road and without CCTV then I use both locks

(paranoid? Oh yes!!!!

but I would hate to have a bike stolen)
I also use pitlock skewers on both wheels and a superglued ballbearing technique to secure my handlebars, saddle and seatpost
Bournemouth is not one of the major bike crime towns, nevertheless, there were 1500 bikes stolen last year and I would hate to become another statistics.