Seems pretty clear to me.
Reserved a Seat - Paid £5.
If you don"t turn up and pay before the start time...you"re out and your seat is up for grabs first come, first served.
Pre-paid / Allocated a Paid seat.
You"re in UNLESS the venue requires that you turn up and confirm your ID in some way.
At least that"s the way I read it.
Perhaps what needs to be clarified is the venue"s tourney registration requirements, I would have thought a phone call could sort that out.