Surely Landlords are reminded by their competent person and having appropriate procedures and systems in place.

I'm absolutely with Kate on this one. Legionella risk is covered in law by COSHH & HASAWA; it is the employer's duty. That duty may be contracted out to a third party, such as for example your commercial landlord, but the tenant in this case is the employer, and is the accountable party. We rent over 300 small shop units, and we carry out our own risk assessments and our own programme of risk control; this I think is normal, John

Thanks for the comprehensive replies and link. It sounds like an examination of contracts is in order ahead of risk assessments, as although in most cases we are the "persons in control" we are excluded from many parts of the buildings including loft spaces where tanks could reside. Also calling them high street shops might have been a little grandiose for what they are, many times the landlords are sole traders/persons and the agreements are skimpy (we don't get wheeled in until the ink is dry and the shop ready to open, another pet peeve). Having said that many are so small scale they rely on instant heaters at the point of use which is in our favour.

Sounds like you've got the advice you needed. The 'Shared Premises' section towards the end of HSG274 Part 2 is the bit you should pay heed to. You're an employer therefore you have duties, your landlord rents out the space, s.3 HASWA applies, and they have duties too. You just need to figure it out and agree where those duties start and stop between you. In practice I seriously doubt it'll be covered in the lease by default (it rarely is in my experience).