I wish to fly into Bristol (EGGD) in a Microlight.
I can see they have a VFR approach procedure here. Can I do this? If so, what are the prerequisites? Assuming filing a flight plan is one of them.
VATSIM is not a good place to look for information on real-world flying. The authoritative source for what you're looking at is the UK AIP. Here's the Control area chart for Bristol. The textual information states
VFR and Special VFR aircraft will usually be instructed to route via one of the Visual Reference Points (paragraph 5 refers), not above altitude 2000 FT (aerodrome QNH).
Further info also states
Due to restricted GA parking, operators of inbound GA flights must notify handling agents with expected ETA and duration of stay. Handling mandatory
That should give you a pretty strong indication that
There is nothing (except ATC clearance obviously) stopping you from flying into controlled airspace in a microlight with an NPPL. There is no pre-requisite to file a flight plan, as far as I'm aware.