I'd suggest more than 6mnths bank statements .... preferably those showing the time when he was employed, and was having a salary paid into his account.
I'd also suggest including the pay slips from this previous job, along with the most recent.
I'd then include a covering letter explaining how....
"I used to work for XYZ firm (from x/2005 - y/2010), and was paid £xxxx per month (as evidenced by included payslips), but I was made redundant, and have recently started a new job at ABC firm, which is paying me £xxxy per month. Please find attached my recent payslips & terms of employment/contract".
