Excellent and correct advice from driver.
A landlord requires a key in case there is an emergency: water leak, fire, gas leak (obviously where there is gas) or in case the tenant has, for example, died and the landlord needs entry.
You should write to your landlord and quote the RTA 2004 section 12:
12.1.(a) allow the tenant of the dwelling to enjoy peaceful and exclusive occupation of the dwelling,
and
16 (c) [The tenant shall] allow, at reasonable intervals, the landlord, or any person or persons acting on the landlord’s behalf, access to the dwelling (on a date and time agreed in advance with the tenant) for the purposes of inspecting the dwelling,
Failure of the landlord to adhere to section 16 (c) renders him in breach of section 12.1.(a) by depriving the tenant of his peaceful and exclusive use of the property.
I advise that you put your complaint in writing (keep a dated copy) to the landlord (his address should be on the lease) so that if he does enter illegally in the future, you have proof that you have already advised him (or any of his agents) not to do so. You could then make a claim with the PRTB for illegal entry.
Unfortunately, you may have to take time off work (as would any house owner) to accommodate tradesmen's working hours, usually 9a.m. to 5 p.m.