Laravel 5 - Validation regex failing

I am trying to validate UK postcodes inside of a Laravel Validation regex like this..

'postcode' => ['required','regex:/^[A-Z]{1,2}\d[A-Z\d]? ?\d[A-Z]{2}|GIR ?0A{2}+$/']

The regex comes from the post at UK Postcode Regex (Comprehensive) and is..

^([A-Z]{1,2}\d[A-Z\d]? ?\d[A-Z]{2}|GIR ?0A{2})$

The regex works when run on https://regex101.com/r/ajQHrd/15 for the test postcode RT4 5GJ but it fails in my Laravel app.

I am assuming this is just my implementation within Laravel, can anyone see what I am doing wrong?

via Chebli Mohamed