"Temperatures in Britain will soar to nearly 21C later this week despite parts of the country having seen lows of -7C since the Easter bank holiday heat wave."

For centuries, marine species have moved around either by hitching ride on the hulls of ships or as stowaways in ballast water. In many instances, species have been deliberately introduced for aquaculture or other commercial purposes.

Scientists say water temperatures are as much as 3 to 4C above the average for this time of year in some areas.