Visa ; 4th Time

Hi all

My Gf has had 3, 6 months holiday visas for England

The last one she got was valid from ; Sep2007 –Feb2008 , she came to England in September and returned to Thailand in Nov2007.

My question is , when can we reapply for a new 6 month holiday visa , do we have to wait 6 months from the date of her last visa or the date when she returned to Thailand ....or neither ??

Also , I’m interested in the opinions of others on what would be my chances of getting a 2 year holiday visa . i don’t want to marry yet , I don’t want to settle in England with my GF , i like my 6 months here and 6 months in UK. I’ve had no problems in the past getting the 6 months visa’s , i have been with my GF for 6 years now.

Thanks