The government wants all council tenants earning more than £30,000 (£40,000 in London) to pay the local market rent for their property, although they would prefer them to move into the private rented sector.
In my neck of the woods (south Oxfordshire) the rent for a 3 bedroomed family home starts around £1,000 a month, plus another £600-700 a month in council tax. A family will need to pay a minimum of £1,500 a month from a gross take home pay of £2,500 a month, probably £2,000 after tax and NI, just for their housing. That leaves approx £500 for fuel, food, clothes, travel etc etc etc.
I can see good reason to have some upper limit, but £30,000 is far too low.