The UK Civil Aviation Authority Air Travel Organisers Licensing Regulations 2012 include the following excerpt;

ATOL REGULATION 11 – EXEMPTIONS FROM THE ATOL REGULATIONS

06/2102 – WHOLE PLANE SALES EXEMPTION

(1) Subject to paragraphs (2) and (3), the Civil Aviation Authority, in exercise of its powers under Regulation 11 of the Civil Aviation (Air Travel Organisers’
Licensing) Regulations 2012 (“ATOL Regulations 2012”), exempts any person
who makes available flight accommodation consisting of the entire capacity of
one or more aircraft to a consumer (as defined in the ATOL Regulations 2012)
from the need to hold an Air Travel Organiser’s Licence.

Full details of the Regulations and this Exemption can be read or downloaded here;

http://www.caa.co.uk/docs/33/ORS3.pdf