OP, there's a lot of really shitty advice in this thread by the usual suspects.
1. Unless explicitly catered for in your contact (which I would be amazed about, and even it would probably be unenforceable), an offer or advertisement to sublet is not a breach of your contract.
2. To regain possession by force without a tenant having been in breach of the contract would put the landlord in breach of same tenancy.
3. You need to very calmly and clearly say to the landlord an advertisement in airbnb does not constitute a breach and even the threat of being kicked out is an interference with your quiet enjoyment of the lease. If he persists in his threats, that you will take further legal action against him.
4. If you come back after Christmas to find your stuff outside the flat with the locks changed, you call the police first, show them the lease and call a locksmith to grant you access. If someone else is physically living in there, then find a modestly price alternative accommodation until you find something suitable. You will have a very strong claim for the amount of costs you incur in this regard. You will need to notify the landlord that they are in breach of the tenancy and you will probably need to lawyer up and sue them.
At this stage, don't start getting scared. Just act like an adult and tell the landlord to (1) go fuck himself and (2) have a merry Christmas.