Eviction Process

I have a tenant who's tenancy agreement ran out last February and I didn't renew it as she owed me some arrears, she has now paid those off but has built of new arrears. Her tenancy is a standard AST.

I get the main part of her rent direct from the council and the tenant should pay £25 per week, she doesn't. Currently she owes £160 and pays when she can borrow it off someone.

Under what process can I evict her please?

Thanks
Alison James