In article .com,
writes
Hi! I want to put a lock on my back gate. I want for it to be keyed
with a 'yale' style key (whatever the correct name for that is). I
need for it to be lockable/openable from both sides. Now, here come the
curve balls...

The backset of the lock needs to be greater than 65mm preferably more
though, to be fair 100mm would be enough :-)

Because this is just a gate (and the 'Z' frame is only about 1" think)
it will be difficult to fit a standard mortice lock. So I'm thinking
that a rim lock may be best - or, at least, quite a thin lock.

Because I don't want to carry a chunking great chubb key around just
for my back gate, I'm thinking that a suitable new fangled euro lock
may be available

If possible, the lock would also have a normal handle for opening the
gate too (does this make it a 'sash lock'?).

If the light key is the leading factor then a euro cylinder sashlock is probably
your closest fit but be aware of a few snaffus:
The sashlock is designed for a well made, close tolerance door so won't work
as well in a gate where it may be a sloppy fit and subject to movement giving
poor latch action & reduced security.
The shortest double keyed euro cylinder is about 65mm and it is a good idea
not to have too much poking out of the door, so you'll likely need sandwich
plates to beef up the thickness on both sides.
I haven't seen one of these with the backset you describe, a 3" lockcase will
have a backset of about 2 1/2", just under your 65mm requirement so you'll
need to work on that.
Be prepared to lube the lock/cylinder a lot as they will see a lot more moister
on the gate than they would in a domestic door.

If you're using this gate a lot or taking the key with you when you go out I can
see that a small key and ease of use is a important but if the gate is less
travelled then you may prefer to use a normal gate type latch backed up with
a surface mounted bolt and padlock. This would be on the inside but could be
accessed from the outside by a small cutout in the door, y'know a hole just
big enough for a hand and the padlock dangling half way into the hole.

Here's a cheap source for locks & cylinders:
http://www.londontools.co.uk/acatalo...ice_Locks.html
UNION MORTICE 78mm & 65mm Sashlock Case Only Ref: J-L2249, half way
down the page £16.25
http://www.londontools.co.uk/acatalo...Cylinders.html
ZONE CEN Grade 4 Euro Double Profile Cylinders--1500series Ref: 1500 DP,
at the bottom £8.87

If you can put up with a large key then a surface mounted sashlock could
work:
http://www.londontools.co.uk/acatalo...Rim_Locks.html
Union Lever Rim Deadlock Ref: J-1445-BJ-51, about a third of the way down
the page £10.67

See also Union Drawback Rim Lock Ref: J-1332-WE on the same page (half
way down). It is expensive (£38.78), fails your backset and is slam locking (no
latch handle) but it is suitable for thin doors and looks as if it might work with
some effort.
--
fred