i want to change my passport to my married name

It shouldn't matter how long you have been married as long as you have proof of your marriage. Take your Marriage Certificate, together with your Birth Certificate and Passport to whereever they issue Passports in the U.K. and it should be a fairly simple procedure to have it changed into your married name, I think that the documents mentioned would be necessary so if you take them, then it is possible you might save having to go back again. Good luck. :)