Tax code may not change, but there are tax advantages to being married. I had some property to sell that would have been liable for capital gains tax. To avoid inheritance tax and make capital gains tax savings I got married, transferred the house into joint names (transfer between spouces is inheritance tax free) and then claimed the capital gains tax allowance per person (so around 20k instead of 10k), making a saving of around 3k :)

Your tax code will be the least of your worries once you are married. That ring on your finger allows your wife to apply taxes the HMRC could never dream of...and she will get away with it too :((

Unfortunately, as Brewerdave1 has said, Married Mans Tax Allowance disappeared many moons ago