Tenant not removed property not cleaned and not yet returned keys

Well, what can I say, I'm surprised! I note they still state: "But landlords should still be cautious and end the tenancy using the correct court procedure of obtaining possession."...but then they continue to outline a process to obtain possession using an incorrect, unlawful procedure. Very strange and surprising. As I said before, it may be a practical way, but it's not legal.
Some food for thought when things aren't done correctly and landlords do get caught:
http://nearlylegal.co.uk/2016/08/landlords-behaving-badly/

Reply to the comment left by "Paul Franklin" at "02/09/2016 - 16:03":

Do you want the abandonment procedures (from the 2016 Act) to come into force or not?

Well if they do it might be easier and save on court fees.

Would be nice to have something that's clear for everyone rather than these 'grey areas' and essentially made-up procedures that basically just limit risk.

Going back to the subject of abandonment and implied surrender as the law currently stands, housing solicitor Tessa Shepperson says, "There is a legal rule which states that if the conduct of the tenant is inconsistent with an intention to continue with the tenancy, this will be considered to be an implied surrender of the property, which the landlord can accept by going in and changing the locks."

She makes the point that is the conduct of the tenant that makes the situation a surrender or not, which is why this is such a tricky subject - it really is down to the landlord to judge the tenant's intention.

Her article can be read further here. The discussion she has with Ben Reeves-Lewis in the comments at the end are especially worth reading.

Well in this case Mandy by not giving back the keys and not moving his stuff out I wouldn't risk the informal abandonment procedure.

My interpretation of the facts as set out in the question is that the tenant is in the process of moving out having agreed an end date by either having been given notice by the landlord, or giving notice themselves. The tenant has physically left the property, but has not yet moved ALL their possessions (probably left stuff they don't want, or stuff which wasn't essential for the initial move) and are using the LL's property as storage whilst they get sorted. (Hence the promises made and broken to get the property fully cleared & cleaned and return the keys)...

As the LL is in communication with the tenant he surely has been made aware by the tenant as to whether they have left the property and obtained a new one, but the fact that he hasn't yet given the LL back possession of the property would in my view make the tenant liable to continued rent charges whilst they maintain control of the property.

In this position I would make that clear to the tenant. If they are aware that each day they delay handing back the keys they are being charged rent (probably whilst they are paying rent on their new property) they will stop seeing your house as cheap storage and hurry up and get it sorted.

You will prob find that they won't clean the place, and will leave behind things they no longer want. Document everything left behind, and the condition the property was left in (including dated photos) and invoices for any rubbish removal and cleaning costs if necessary for any claim you may need to make against the tenants deposit. I would certainly include a pro-rata rent claim for the extra days they retained possession of your property.

You are unable to relet the property property whilst the tenant retains control over it, regardless whether they are physically sleeping there. It's not able to be let with someone else's things in it. Whilst they continue to keep the keys and say they are coming back to complete the move it is likely that the tenancy has not yet legally ended. I have read on Tessa Shepperson's Landlord Law Blog about a former tenant who re-entered the property with retained keys (AFTER the new tenants moved in) to pick up items they'd left in the property when they moved out!!

Make sure you keep a record of all conversations with your tenant, date, time, what was said by both parties in case you should need to justify your actions, and ensure any demands by you, or deadlines given are in writing (even an email).

If your tenant insists the tenancy HAS ended and that they shouldn't be charged further rent, then get them to put it in writing, along with their agreement that you can remove the items from the house and relet the property. You can then at least move forward and offset any essential costs incurred by the tenants actions/inactions via a claim against the deposit.