This is the wording in the Act
“Some rent lawfully due from the tenant—
(a) is unpaid on the date on which the proceedings for possession are begun; and
(b) except where subsection (1)(b) of section 8 of this Act applies, was in arrears at the date of the service of the notice under that section relating to those proceedings.
Now lets pick it apart.
If you have 2 months or 8 weeks arrears as per Ground 8 then it stands to reason that you also have Ground 10, an indeterminate amount of arrears, different from that prescribed by Ground 8 but arrears nonetheless.
This is a discretionary ground however, so as with all of them, even if the ground is proven and the arrears exist the judge has to consider whether or not possession is reasonable.
Housing Associations use Ground 10 a lot, seeking as they are, merely a Suspended Possession Order to hold over the tenant while they clear the arrears a week at a time.
The case of Hayman v. Rowlands (1957) confirms the logic that if the arrears are cleared by the date of the hearing a judge should consider it unreasonable to grant possession but there are other arguments raised in the cases of Bird v. Hildage (1947) and Beavis v. Carmen (1920) which took the view that it is the point at which the possession proceedings are issued not the date of the hearing which is the cut-off date to clear the arrears.
So a last minute scrabble down the back of the settee for loose change the morning of the hearing might not suffice.
However the overriding factor here is that the judge still has to find it reasonable to grant possession, regardless of whether the arrears were cleared on the day of the hearing or before.
A judge may be swayed in their thinking if the tenant repeatedly runs up arrears but clears them at the last minute, the landlord would certainly have good grounds for seeking costs against the tenant where this happens.
Defending this ground
Advocates should check the figures being claimed first and foremost. It is not unusual for both parties calculations to be wildly off the mark, even to the point where it can be the case that the tenant has actually overpaid.
I have been involved in several of these over the years.
Also, watch out for grounds for counter claiming for disrepair or breach of covenant for quiet enjoyments as any damages can be offset against the arrears themselves.
Look to income and expenditure as well as any Suspended Possession Order will be on terms of rent plus a certain amount off of the arrears and you need to show that the tenant can maintain regular payments on any offer they make.
On this same point, if you are going to make an offer to the court make sure it is one that the tenant can afford.
Numerous times I have been involved in untangling a mess after the tenant made an offer in a last minute panic to clear the arrears by instalments that just weren’t feasible in the first place and you have to then go back to court and explain why the tenant didn’t adhere to the terms, running the risk of wearing out the judge’s patience.
In representing make sure that the judge knows the reasons for the arrears having accrued. Housing benefit delays, income fluctuation, family emergency are all valid and reasonable arguments. The tenant having just come back from holiday is a more difficult one.

Tessa
“Housing benefit delays, income fluctuation, family emergency are all valid and reasonable arguments”
Do you mean for the tenant to put forward in mitigation?
Not valid enough to emphatically defeat a possession claim but enough of a defence to seek adjournments and suspensions.
As is the case with the Home office in immigration status issues the housing benefit teams can often be at fault. Not always but often enough and if the reason is genuine it counts towards a defence on reasonableness, as do emergencies and income fluctuations, again I emphasise, ‘If genuine’.
The point of the section on defending claims in my article above is that the defence advocate needs to concentrate on the factors that influence a judge in consideration of what is reasonable, a defence not open on Ground 8 claims where, if my information is to be considered reliable, fluctuates even on mandatory grounds in some courts
I hesitate to raise this but it is “unpaid” not “arrears” in HA 1988 see..
http://www.legislation.gov.uk/ukpga/1988/50/schedule/2/part/II/crossheading/ground-10
– a rather more important distinction for Grn 8 where, if rent is due 1st of month then 2 months would be due on 2nd after 2 missed payments (1 month 1 day), whilst most people would say 2 months arrears not until 2 months