There are no regulations in the UK for minimum design capacities for various buildings, which is left to the judgement of the electrical designer.
This is not the case in all inspection jurisdictions. In some areas codes or standards may require minimum stated capacity in order for a building to be considered adequate for its intended purpose. Also the UK Electrical Supply Act imposes maximum permitable harmonics back on to the supply authorities network.
Hence, as an early task in assessing load requirements should be a code investigation to determine: