Agreeing on fixtures and fittings on a property subject to an AST agreement

As part of a Tomlin Order I have made an offer to buy a property that has a continued AST agreement with tenants. The price of the property was agreed as a legal settlement between myself and the Landlord (the vendor). I agreed to pay for the property as is and with the tenancy agreement in place.

The agreement includes a clause for us to agree a sum for the furniture, fixtures and fittings remaining in the property. This was originally to negotiate reasonable payment for their furniture or to replace it before completion, so as not to inconvenience the tenants.

However, the draft contract arrived today with a draft fixtures and fittings and contents schedule for approval. The Vendor is now excluding virtually everything from the agreed property purchase price, including the kitchen sink! He claimed to be desperate so as not to inconvenience the tenants by leaving them without furniture, but the fixtures and fittings list is exhaustive and includes everything in the fitted kitchen, all carpets, bathroom appliances, sunken ceiling spotlights, lights, burglar alarm, TV aerial etc. He is demanding £12,000!!

I could call his bluff and refuse to accept or agree payment for his schedule, but he could then remove the lot from the property before completion. Surely this would be a breach of his landlord-tenancy agreement where he could potentially leave the tenants with only a shell if I don't agree to his ransom charge?

I would be grateful for some advice. I need to know if he can make such an unreasonable demand considering the property must be delivered up in no worse condition than as shown on the schedule of condition that he agreed with the tenants.

Thanks for your help.