Hi jabz i recently got my visa and i am in the uk and i relied on third party funding from Pakistan. Its not a problem if you are relying on third party funds if you need the sample documents please check this link out
http://www.immigrationboards.com/viewtopic.php?t=137118 please kindly read the policy guidelines word by word if you need to make a successful application. I know that the banks in Pakistan may not write the exact letter but make sure you include every thing as required by the policy guidance as my first application was refuse just on the basis of the bank letter. I even submitted a letter from the bank that its their policy that they cant write my name on the third party bank letter but the home office said that its the bank policy not to write but we do need it because its our policy. My friend my third party bank statement balance was almost 7.2 million pounds but the home office did not care. They only follow the immigration rules and policy guidance. so make sure you follow that as well. If you need any further information please contact me.