Lock Recommendations

I'm looking to get a U lock or chain that can be carried around during the day. I have a Kryptonite New York 10/10 rating but it's heavy carrying it everywhere for locking the bike at the various offices I work between in London.
Although I want to keep the weight down I don't want it to be too make it easy for the thieves .
I'm interested to know what people recommend especially anyone who is carrying a lock with them all day, couriers etc.
Thanks
Steve

http://www.bikehacks.com/bikehacks/2014/10/quick-caps.html

Primary thread.
https://www.lfgss.com/conversations/144109/

Secondary locks, or lighter weight ones.
https://www.lfgss.com/conversations/194773/

Weigh up where will the bike be locked, how long will it be left, how much do you value it.

I've got one of these for sale, but am just waiting back on a reply. It's weighs about 500 grams less than the Kryptonite.

http://thebestbikelock.com/best-u-lock/abus-granit-x-plus-540-review/

Poetic, thanks but before I do anything I have to see if I still have a lighter D lock I had. Haven't seen it for years so will have a look this weekend to see if its buried in the garage.

More for locking upfor a ten minutes outside the coffee shop on the commute in. Then inside a locked bike shed once at work. How much is it worth? not much but I'd still not want it nicked because I'd have to replace it and probably with something that costs me more or I value more.

I do have a lighter D lock somewhere kicking around, key is on the bike key set but haven't located the lock yet!

Light lock for coffee shop then leave a heavier lock in the bike shed. No need to carry it around if you lock it there all the time.

If you can find one the original Abus Granit futura is less than 700 grams and is very well built, perfect for zipping around town with and quick lock-ups. I have this and the Granit 540 @Poetic is selling and it covers all my needs. I don't tend to carry both if i'm leaving the bike for longer periods as the 540 generally covers the frame and wheels if i pop the front off. The easyKF bracket works well too if you need to lug the 540 around.

Managed to find my lighter weight D lock after virtually emptying my garage so sorted. Thanks to everyone for your advice.