Paul Crowther, deputy chief constable of British Transport Police said: "The new laws that come into place today change a number of issues in respect of scrap metal. First of all it increases the sentences that are available under the existing legislation.
"It provides powers to the police to end unlicensed scrap metal dealers for the first time and introduces a new criminal offence of trading in cash for metal, which is a very significant measure in tackling metal theft at the point where it's sold into scrap metal yards."
More top news
Scotland Yard said two murder investigations have been launched following the separate incidents, which both happened in the past week.
Photos show the extraordinary surgical procedures to remove the growth.
The Met Police says 143 firearms have been handed in at stations across the capital in just seven days, including two antique machine guns.