The ANO Art 126 defines which aircraft require to use a licensed aerodrome in the UK. Art 128 and CAP168 detail how the licensing requirements are met in practice.
Airports provide a published fire category; aircraft are allocated a fire category. Aircraft fire category must not exceed available fire category.
The ability to accept aircraft of a higher category [providing there were no more than 700 in the busiest three months] was removed in 2005. Additionally, the facility to 'deplete' the fire category temporarily has now also been removed. According to 'the book' in the UK, the rule is as in paragraph 2 above.
Airport Licence Holders are required to inform operators and pilots whenever any of the 'notified' facilities/services are not avaialble.
Whether or not a public transport can actually land is probably a grey area with the answer depending on the views of EASA/CAA/JAA/Lawyers/Flight Ops Manual!
Helen