The agency warns, however, that pregnant and breast-feeding women shouldn't eat swordfish, tilefish, shark, or king mackerel and should limit consumption of white, albacore tuna, a commonly canned variety.

WSJ: Guidelines for Eating Sustainable Seafood

King has chronic knee problems which limit his appearances and his call-up angered Spurs boss Harry Redknapp.

BBC: Capello hits back in King dispute

With Jonathan Woodgate still out with a long-term groin injury and captain Ledley King plagued by knee problems that limit his playing time, Redknapp has been keen to bolster his defensive resources.

BBC: Tottenham sign defender William Gallas on one-year deal

But RAC Foundation executive director Edmund King said it would be difficult to set a legal driving limit for cannabis as traces of the drug can stay in the body for up to a month.

BBC: Call for drug-driving limits

"Personally, I think that having some threshold would give some more uniformity to the test, but pragmatically we don't want to limit the sensitivity of tests, " said Prof David Cowan from King's College London, who is in charge of anti-doping at next summer's London Olympic Games.

BBC: Ban on clenbuterol doping drug may be relaxed