As far as I know ALL wood preservatives/ paints/ varnishes are suitable.
Just pop down to the diy store and aks the staff, they will be the ones in the know.
:0)
This is from the RSPB site, noddy:
It is best for the birds if you leave a birdtable untreated. However, it will last longer if you treat it. Water-based preservatives, such as Fenceguard or Sadolin, are less toxic and will not affect the food you put out. The preservative should be thoroughly dry before you use the table for feeding.
Thanks very much!
Not sure how they'll take to the 'Restaurant closed for refurbishment' sign! There's a couple of collared doves doing 'things' on it at the moment (don't they ever stop?) - think I'll have to politely ask them to leave!