Nuisance tenant or unreasonable neighbour?

Other

I have a tenanted maisonette (without garden) on a smart 2010 built small mews development comprising eight other properties, all of which are terraced houses with gardens. An owner of the house directly opposite the maisonette sent me the following email:

"Just a quick note in confidence as I thought you should be aware that the residents in the Mews have noticed that the tenants who are in no:8 (very nice and no trouble at all) but I'm not quite sure if they should be hanging their washing outside on the drive? On a separate note and without sounding like a killjoy, they do also sit out there on sun-loungers with their BBQ - they do live in a flat knowing they haven't got a garden after-all. Just thought you should know."

My AST Agreement with the tenant has a special condition not allowing clothes to be hung from the outside of the property (this has not been taken from a head-lease). That said, the tenant is using an airer on the communal drive as opposed to hanging clothes directly from the property.

The tenant has been no trouble whatsover and, I presume, is making the most of the recent hot weather.

What do you suggest my response should be to receiving the email?

Regards