Art 11 of the ANO
11 (1) The CAA shall:
(a) subject to sub-paragraph (b) issue in respect of any non-EASA aircraft registered in the United Kingdom a national permit to fly if it is satisfied that the aircraft is fit to fly having regard to the airworthiness of the aircraft and the conditions to be attached to the permit;
(b) refuse to issue a national permit to fly in respect of a non-EASA aircraft registered in the United Kingdom if it appears to the CAA that the aircraft is eligible for and ought to fly under and in accordance with a national certificate of airworthiness.
C152 is eligible for a C of A so it's really dead simple. Go to Cessna, get an STC for the mod and then get the CAA to accept it.
After all there's an STC accepted by the CAA for this.
