When asked if there was a specific reason they said they "wanted to see it". Does there need to be any more clearer reason to make such inspection or does "just wanting to see it" suffice?
A landlord can “pop over”
As a tenant you can agree to this request without further formality but here are the legal rights.
If the landlord gives a written notice (emails and SMS count) giving at least 24 hours notice, the time of the visit, who will be making it and why, then they have a right to enter providing the time is reasonable for the tenant. If the tenant refuses because the time is inconvenient, they should propose one or more convenient times. If damage accrues to the property because of a delay, the tenant may be responsible for it.
A landlord may also enter immediately in an emergency such as a fire, a gas leak or a flood.
A landlord faced with tenant that unreasonably refuses entry can get a court order to allow it. Likewise a tenant faced with a landlord who makes voluminous requests for entry (say more than once every 6 months) and thus preventing their “quiet enjoyment” can get a court order to regulate that.