Tenant got planning permission for C2 usage without my knowledge?

1. In Rotrust Nominees Ltd v. Hautford Ltd (2018) EWCACIV765 the Court of Appeal found that a landlord was unreasonable in refusing consent. The tenant was looking to apply to the local authority for a ‘change of use’ in the rented property.
Check out this case law. Its not identical. But will inform you about landlords need to "act reasonable" when tenant requests consent for change of use.
2. The tenant needs consent from the landlord. Any changes need prior consent in writing with agreement to return property to original state. Check your lease, it should contain this requirement.
Sounds like the tenant didnt act correctly. But you might not be able to reasonable refuse it, even if they did ask.
Best outcome would be to get written agreement that the charity will return porperty to original condition including planning status.
If you need leverage to get the charity to agree. I would write to planning and state no consent was sought or given. It might delay the charity plans enough for them to agree.

LPAs don't generally care about private law issues when considering PP applications. They'd probably be challengeable decisions if they did.

When submitting the planning application, the applicant should have sent you a notice as owner of the property and will have ticked a box to say that they have.
That said, would it make the application unlawful to make it invalid or change the decision, made on planning criteria - I don't know - may be worth looking into.
Also, what does it say on your tenancy agreement/lease with them about planning applications or use of the property?. Could it be an opportunity for negotiation?
Under your agreement, will they also need your consent for alterations? That's a separate matter from the planning consent, and just because they've got planning consent they cannot assume they have your consent to works. If they invest in the property they may also be inclined to rent it for a longer period of time. Do you have a comprehensive check in inventory with photos showing the condition of the property when they took possession?

Could the new consent enhance the value should you wish to relet or sell to another institution?

There could be some positives in the situation.

Reply to the comment left by BRACKS Mead at 26/09/2023 - 10:18The Supreme Court did overturned the decisions of the High Court and the Court of Appeal (in that case, Sequent Nominees Ltd (formerly Rotrust Nominees Ltd) v Hautford Ltd [2019] EWCA Civ 765)
SC ruled that it was reasonable for L to refuse consent.

On a slight tangent, if you have one, I would check with any mortgage lender whether this is OK with them.

Reply to the comment left by Michael Freer at 26/09/2023 - 12:15
... you may want to check insurance too

If its now a business, tell them you want a new contract written up i.e. a FRI contract then increase the rent to suit it, then you can borrow more money against it. Then you are not a Btl landlord any more and can evict them alot quicker as a business if they stop paying.

Planning docs are all online, so you can download copies of all docs they submitted, including any that say they informed all interested parties. As others say, your building insurance is likely invalidated. And yes, it could seriously devalue the property.

Wow! I am no legal expert but this seems very high-handed behaviour if it is a registered charity. They may well plan to house tenants who have compromised mental or physical health or other impairments and expect to add disability aids etc to the property. Sounds like you really need to seek a new rental agreement to ensure that you are absolved from accidents to and damage caused by the occupants, and that the charity is entirely responsible for managing and reinstatement of the property. Neighbours may also raise concerns if they have not been consulted about it's change of use.

First thing I'd do is look up the charities annual return and see what their history and finances are like. It might just influence any decision you make!