How much would I make from £1100 rent?

[mymonkeymycircus]

Due to circumstances we have the opportunity to rent out a mortgage free property we own.

We'd do this through an agency.

Would charge about £1100 a month

How much realistically after agent fees, tax, other expenses would we actually get?

Is £800 unrealistic?

Any advice helpful

Don't rely on an agent to manage it - you need to oversee the legalities with a fine tooth comb as the buck stops with you if there are issues down the line. Look ahead to the tenancy legislation changes coming in soon. You won't make a lot of money and may well lose money unfortunately. I'd look into stocks and shares instead also.