Jen, regarding the financial requirement. Your fiancée only needs to show his salary meets the requirement of £18600 per year gross.
He needs to provide 6 months payslips and the corresponding 6 months bank statements to show his salary going into his bank A/C
He needs also to have a letter from his employer stating how long he's been employed there, his employment basis and confirming his salary.

There's no need to be concerned with income support levels.

BTW, that P60 will not be of any use as it only confirms his income between April 2012 and April 2013 so it's already almost a year out of date.