You can let it expire; I finally found this out after phoning the CAA several times. You have up to about two years to renew before having to go back to the Belgrano; might be longer, I can't quite remember. Also, you can now use a Class 1 as a Class 2 for the length of time a Class 2 would be valid, as was true in the past pre-JAR. The trouble is, not a lot of AMEs know that. I had to persuade mine to phone the CAA to get this confirmed; then all he had to do was stick a label on my Class 1 saying it could be used for Class 2 privileges and validity.