Guarantor for tenancy already running?

My guarantor agreement, which I get signed and dated by the guarantor(s) before the tenant(s) signs their tenancy contract state, (a tad long wided though lol)

“That the tenant(s) shall pay the rent hereby reserved on the days and in the manner set out in the Agreement and shall perform and observe all the agreements on the part of the Tenant(s) contained in the Agreement or documents annexed to and

That in the case of default by the Tenant(s) in the payment of such rent or in the performance or observance of such agreements as aforesaid I/We shall pay and make good to the Landlord on demand all losses damages costs and expenses thereby arising or incurred PROVIDED THAT any neglect or forbearance of the Landlord in endeavouring to obtain payment of the rent reserved by the Agreement when the same becomes payable or to enforce performance or observance of the several agreements on the Tenant(s)’s part therein contained or any time which may be given to the Tenant(s) by the Landlord shall not release or exonerate or in any way affect the liability of the Guarantor under this indemnity and

That the provisions of this indemnity shall apply to any increased rental and/or to any continuation extension renewal or re-grant of the tenancy created by this Agreement whether by operation of law or agreement between the Landlord and the Tenant(s) or otherwise as if this indemnity were incorporated in full in such contained extended renewed or re-granted tenancy (as the case may be) and for the avoidance of doubt the Guarantor hereby agrees with the Landlord that the Tenant(s) shall pay the rent reserved by such continued extended renewed or re-granted tenancy (as the case may be) and shall perform and observe all the agreements on the part of the Tenant(s) therein contained.”

Or could draft something similar. Cannot see why you cannot get guarantor(s) during the lifetime of the tenancy BUT I would also give them copies of the current tenancy and any Tenancy Interpretation, Inventory (which could be updated to guarantor agreement date if under an inspection and counter-signed and dated by the tenant(s), EICR, EPC, How to Rent, Gas Safety Certificate and deposit info (certificate and Prescribed Information)

What incentive is there for any potential guarantor to agree once the tenant is living there?

I had been advised by my property rental manger to get a guarantor which proved worthless so please look into it as I had to use the deposit for last rent not paid and the house was left in such a mess it costs me ££££ to get my house back on the market and couldn’t claim any thing from deposit as it covered rent not paid ( it’s all about there tenant these days extremely unfair for the Honest landlord!!!