illegal immigrant getting married help

hi new member here would appreciate if someone guide me to right side
so i came in the uk in 2007 as a visitor visa and then applied for asylum which got refused several times and they put me signing every month which i went to sign for few months then didn't go there to do soo...now i got a girlfriend who is uk born and raised she got own place and earns more then 40000 ... now we are thinking to get married here in uk soo here are few question

what would happen when we go to registrar office and which documents i need to provide
how many chances are there ukba to show up on wedding day
my passport is expire soo would i need a new one to get married
what kind of proof of address do we need

thanks in advance

There may be good chances that they will attend without an invitation. Perhaps a solution is to invite them as guests?

Under what circumstances you applied for asylum?
Why did your asylum get refused?
Did you appeal the refusal?

In order to marry in the UK you will have to register your intent to marry with a Home Office designated Registry Office. The Registrar is then legally bound to notify the HO who can then extend the notification period from 28 to 70 days in order to interview you both separately before the wedding can take place. You are likely to be either detained at the interview or as Vinny has suggested, the Border Police may well arrive on the day of the wedding and remove you before the ceremony can take place. Read the circumstances in Vinny's link.