Television licensing officers caught 900 Croydon residents watching TV without a licence in the first six months of 2011.
The borough had 500 more cases than Bromley, 300 more than Sutton and 500 more than Lambeth.
Pauline Gillingham, TV Licensing spokesperson, said: "While the vast majority of people in the UK pay their licence fee, to be fair to those who pay, we have to be firm with those who try to get away without paying.
"We take TV Licence evasion very seriously and we will not hesitate to prosecute if people continue to break the law."
They are among almost 197,000 people caught across the UK during the first half of this year.
The average evasion rate remains at a low of just over five per cent, meaning that almost 95 per cent of properties are correctly licensed.
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