Evans Cycles

AFAIK, that's my understanding, compound by the complication of some customer's bike may have part fitted that have yet to be paid for.

Stealing, in other words.

Not really. Stealing requires an intention to permanently deprive the owner of the item. The landlord would argue they aren't doing this as the items are just caught up in Evans not paying their rent and they'll get them back when the issue is resolved. In other words, it's not the landlord's responsibility to sort out items that only Evans knows the proper ownership of.

Anyway, it's shitty for all involved.

If the landlord has taken possession of the premises, by not letting customers retrieve their bikes aren’t they withholding property that isn’t theirs? Stealing, in other words.

Depends how they gave notice, they most likely had an agreement with the previous owners of Evans and have sent multiple notices to the old addresses which have obviously been ignored. If all they had in the way of communication from Sports Direct was show boating and demanding lower rent then locking the premises and taking everything on site as payment of rent due makes sense. I've had to arrange similar in my past job for landlords of an office block, locked out a solicitors firm and must have caused countless damage and disruption to clients they had by extension but if they made a choice to ignore notices continue trading and not vacate or communicate what are they to do.