You are allowed to leave your home to make pick up a purchase or obtain services if you have already made it. Its an explicit exemption.
(h)to collect food, drink or other goods which have been ordered from a business, or to access goods or services which are provided in any way permitted by paragraph 12 or 13; or
You are however discouraged from doing so.
And whilst you might be able to argue that the hire of a venue is 'making a purchase or obtain a service' merely viewing and not signing on the dotted line makes that a problem. You are NOT going to pick up a purchase.
The house sale exemption can not be applied as it explicitly states residential property
(f)to undertake any of the following activities in connection with the purchase, sale, letting or rental of a residential property—
The wedding exemption is explicitly restricted to attending a wedding:
(11) Exception 8 is that it is reasonably necessary for P to leave or be outside P’s home to attend a marriage ceremony, a civil partnership ceremony or an alternative wedding ceremony permitted under paragraph 6(11).
More to the point if you look at the restrictions, leisure venues and facilities are closed to the public.
The exemptions are:
(4) A place is a public outdoor place for the purposes of this paragraph if it is a public outdoor place other than a fairground or funfair and—
(a)no payment is required by any member of the public to access that place, or
(b)the place falls within one of the following categories—
botanical gardens,^
gardens or grounds of a castle, stately home, historic house or other heritage site.
Note - nothing indoors.
Under restricted businesses it states that you can carry on with other aspects of the business BUT:
(2) Paragraph 10(1) does not prevent a person responsible for carrying on a restricted business or providing a restricted service (“the closed business”) from—
(a)carrying on a business which is not a restricted business, or providing services which are not restricted services—
(i)in premises which are separate from the premises used for the closed business,
It can't be on the premises which are closed by these restrictions.
Weddings Ceremonys ONLY are allowed. Any ONLY in exceptional cirumstances. Otherwise they are restricted. That means wedding venues are not allowed to operate UNLESS there are exceptional circumstances.
All wedding venues that I can possibly think of therefore fall under restricted businesses and since you are explicitly not allowed to operate any other part of the business on the premises of restricted businesses, I would therefore conclude that going to visit a wedding venues is most definitely not excepted under any of the regulations and indeed it is actively prohibited.
I personally would be asking the business concerned here which regulation exception they are operating under and what exemption there is for you to enter premises which are closed by law.
I have gone through this with a fine tooth comb, and genuinely can not see any way you can argue a loophole tbh.
Its not legally allowed.
Besides as others have said, you should be trying to refrain from doing things unless necessary anyway. And this definitely falls under unnecessary.
The venue could provide virtual tours but they can not legally show you around from what I can see as this counts as a closed sector.