If your Class 1 expires on 1st July, why don't you renew it now? As per JAR-FCL-3.105, you can renew a valid Class 1 medical certificate in 45 days prior to expiration date. New certificate would be of course then valid until 1st July 2011.
Of course, I'm not familiar with UK CAA, but this is basic JAR-FCL-3 rule.