Go see an AME - ask them about the requirements for Class 1 and ask whether you would be eligible. The regular AME's who do the Class 2 PPL medicals are usually also capable of doing (non-initial) Class 1 renewals too, so they will know the deal. Better to spend £300 on a Class 2 and good information than to spend £700 on a class 1 which may result in your class 2 being withdrawn!
https://www.caa.co.uk/aeromedical-ex...e-material-gm/
CLASS 1 - AMC1 MED.B.070
(d) Refractive error and anisometropia
(1) Applicants with the following conditions may be assessed as fit subject to satisfactory ophthalmic evaluation and provided that optimal correction has been considered and no significant pathology is demonstrated:
(i) hypermetropia not exceeding +5.0 dioptres;
(ii) myopia not exceeding -6.0 dioptres;
(iii) astigmatism not exceeding 2.0 dioptres;
(iv) anisometropia not exceeding not exceeding 2.0 dioptres.
(2) Applicants should wear contact lenses if:
(i) hypermetropia exceeds +5.0 dioptres;
(ii) anisometropia exceeds 3.0 dioptres
(3) An evaluation by an eye specialist should be undertaken 5-yearly if:
(i) the retractive error is between -3.0 and -6.0 dioptres or +3 and +5 dioptres;
(ii) astigmatism or anisometropia is between 2.0 and 3.0 dioptres.
(4) An evaluation by an eye specialist should be undertaken 2-yearly if:
(i) the refractive error is greater than -6.0 dioptres or +5.0 dioptres;
(ii) astigmatism or anisometropia exceeds 3.0 dioptres.