Formal maternity dress to borrow

I’ve got a function to go to soon and I need something smart to wear but I don’t really want to be buying anything that I’ll only wear once and I know this is a bit cheeky of me to ask but if anybody has a size 16/18 nice maternity dress that I could borrow then please let me know. I don’t mind picking it up in London or Bedfordshire because I’m currently living in both areas at the moment. Xx