Buying a house with tenants in

Looking to buy a house.  We are renting.  House has tenants in it who say they will leave on week before our (unextendable and unreproducible) mortgage offer expires.

We don't need to move in immediately on completion.  Our mortgage offer is owner-occupier; not buy-to-let.

We have a solicitor, but I just want to validate that we need to exchange and complete on the same day (or at least exchange and complete within the week of vacation) after checking the tenants are indeed out.

I guess it might be possible to draft a contract that has some contigency in it for the tenants not moving out, but this seems pretty pointless?

there's standard wording that can be included in the contract and the current tenants sign, waiving any rights to occupation on completion and agreeing to vacate. The contract will also provide for vacant possession to be given by the seller on completion.  Your solicitor will no doubt advise...   

What Kimmy said plus you can provide completion is five working days after the tenants vacate subject to a long stop date when you can walk away to incentivise the seller making sure they leave.  An investor seller often won’t give notice to the tenants until a buyer exchanges but sounds like they’ve already given notice.

Also your mortgage lender will normally allow an initial short extension if needed.

Thanks I already have an extension from the lender.  I think given how far rates have moved since the mortgage offer was made it's unlikely they would extend much further.