Hi mrt, I'm a landlord and, although I haven't had any tenants in the past who were entitled to rent allowance, my property has recently come up for rent and all the prospective tenants who have requested a viewing are on rent allowance.
I'm not keen on the idea of being paid in arrears, but am quite happy to accept rent allowance on condition that the tenant signs a consent form/waiver allowing the Welfare Office to pay the rent directly to me and they also pay a full month's rent as a deposit.
Perhaps you could contact landlords in the area you are looking in and explain that you're happy to pay the full deposit and to sign a consent form allowing them to be paid directly.
A lot of landlords will have to re-evaluate the 'no rent allowance accepted' as it's possible that a tenant who has a job at the time of renting may lose their job and become dependent on welfare.
I've also wondered about the legality in terms of equality legislation that allows landlords to state in their ads that they will not accept rent allowance, would have thought this was discriminatory.