M5 is now looking OK as far as Almondsbury. Suggested route from there on Googlemaps is currently M4(Eastbound), M32
I'd say to head down the M5 but keep an ear on the radio
I've just come home to Portishead from Worcester, it's backed up completely from J17 (Cribbs Causeway) to J19 (Portishead), (I went through Clifton to get home), and I'm sure it will get worse before it gets better. That's probably not much help at this stage- only advice is whatever route you're trying, get off the M5 before J17.
I'll be getting the bus to the match later, looking forward to it. Safe journey all who are going, hope you all make it in time.