Thank you everyone for your replies!

I edited the post to clarify that it is a Chelsea home game. Since I don’t want to buy more jeans, I will just wear the casual dress and tights that I had planned. I of course will be bundled up as it is predicted to be around 8 degrees and I will be freezing! We will make sure the my fiancé brings a sweater/jumper in addition to his coat in case they have a problem with his jersey.