Reliable Digital Lock

I'd recommend investing in something by abloy and get sufficient keys cut with it to serve your plotholders plus numerous spares.

I've used those locks for years and they are the dogs pyjamas. Only had experience with 350/362 (the big iron) but a 340 or something would be fine for an allotments.

Yes expensive but if you want something that is going to last you 10-20 years regular use, all conditons. Abloy are the way.

Thanks for the responses. We've managed to get our replacement lock to function by using a squirt of GT85 lubricant and exercising the mechanism. There is no need for intruders to pick the lock or smash it as the site can be entered by climbing over the peripheral fences, so we can't justify an expensive solution. We just want something that works reliably ! Our existing Squire lock cost £30 and comes with a 10 year guarantee, but the first one failed just after a year of use while the replacement started giving trouble after a couple of weeks.
We don't want to go back to using keys, the digital solution is much more convenient - when it works......