I don't believe that's the case, from CAP804 (part L appendices to part-fcl):
(d)6 hours of flight time shall be completed in a multi-engine aeroplane.
1
1. The reference contained in (d) only applies to pilots seeking to conduct a Skill Test in a Multi-engine aeroplane. The UK CAA issued a derogation under Article 14(6) of the Basic Regulation to reflect this.