I'm not sure what differences there are between England and Scotland, but Shelter website may be able to shed some light on where you are.
I recently had a monumental battle with my ex LL, she wanted to take £415 from my deposit and cited a bunch of lies and fabrications to justify that amount.
I refer to your para:
"We took some evening / WE time to clean as much as we could ourselve, and got a cleaning company in for the rest. Had to re-paint the bathroom due to the mold / black fungus. We will have to resand / varnish part of our floorboard at a later date due to the damage (the floors are the main "appeal factor" of the flat) and one of the carpet is stained beyond repair.
We ended up withholding part of the deposit for cleaning and damage (itemised email to tenant to inform her) - £50 for wet vacc rental, £80 for sanding + varnishing costs, £30 for mould / repaint, £60 for cleaning company, "
Firstly the WE time issue... makes you sound entitled, you are earning money, being involved and rectifying properties between tenants is the inconvenience you are being paid for.
I'll not even dignify the comment you just made about "I know tenants are generally a nightmare"....
DH was lax, you got shafted.
That out of the way, you would seem to have legitimate expenses incurred to make the property rentable.
When I went to the TDS in a single claim against my LL, the DPS ruled against her as
- she didn't have a proper inventory, so they would not be able to establish the start condition.
- she didn't provide any evidence to support her claims against my deposit.
OK so you can't prove the state of the flat in the first instance, but you seem to be able to show clear evidence of remedial work, you may have a shot.
As far as the out of date tenancy agreement, again Scotland may be different, but in England a contract that is allowed to continue is referred to as a statutory periodic agreement and the same stipulations as signed for in the original contract apply, save the notice periods, 2m calendar written from you to her and 1m from her to you.
Stained and filthy carpets is NOT fair wear and tear, not when you haven't even bothered to clean it.
My new, fabulous LL has asked that we do not cut anything directly on the formica, so i think you could say that no stilletos to be worn on the wood.
Don't allow yourselves to be bullied, do the best you can to defend this, make an appointment with CAB, consult Shelter Scotland properly and see what they say.
However, the lessons for next time are as follows:
Independent Inventory - signed by tenant and LL
Fully dated photographs of the condition prior to the tenant moving in.
If prior to an inventory you have had a professional cleaning company, then you can present this as part of the tenant pack, so that they know that they have to do the same prior to check out.