having marshalled for many years, MX and road you probably wont get to do WSB or moto GP in your first year at least. there is usually too many volunteers and unless you do every meeting that year for all 3 or 4 days wont qualify, on the other hand NGMCC our local club are also on the look out as ever, usefull to join them and learn your trade
http://www.ngroadracing.org/marshals.htm, will help as Nino , Steve and most of the rest of the NGMCC organisers are highly placed in the organisers of BSB, WSB and motoGP in the UK.