From LASORS (UK)
"Revalidation of a helicopter type rating requires a proficiency check in the relevant type of helicopter within the 3 months immediately preceeding the expiry date of the rating, and at least 2 hours (including the proficiency check) as pilot of the relevant helicopter within the validity period of the rating"
also;
For single-engine piston helicopters as listed below (Appendix 1 to JAR-FCL 2.245(b)(3) refers), an applicant shall complete at least the proficiency check in accordance with JAR-FCL 2.245(b)(1) on one of the applicable types held provided that the applicant has fulfilled at least 2 hours pilot-in-command flight time on the other type(s) during the validity period which that revalidation proficiency check shall carry across. The type ratings for this purpose are:-
Bell 47, Brantley B2, Hughes 269, Enstrom ENF28 and Hiller UH12
Regards,
BC.