In the UK, some train stations have bicycle lockers, such as in Earley or Lancaster. It looks like smaller stations (but not the very smallest) are more likely to have those than larger stations; I couldn't find any at Reading, Paddington, or Birmingham New Street.
But the question is: how do I access those lockers? I couldn't find any relevant information on the websites of National Rail, South Western Railway (manages Earley), or Virgin Trains (manages Lancaster); I only find information about taking bicycles on the train, not parking them securely beyond the useless "you can park your bicycle at the station".
How would I get apply for access to one of those bicycle lockers? Who manages them? Are they by subscription only, or can I rent one for the day if available? With Google Search, I found results for different parts of the USA and for Ireland, but the UK ones remain a mystery.