"The first four months of 2007 are on track with our global forecast for a warmer than average year, but the cool La Nina event developing in the equatorial Pacific could prevent 2007 from being the warmest-ever year," David Parker, a climate scientist at the Met Office said.

La Nina, or the girl, which recurs every few years, is characterized by unusually cold ocean temperatures in the eastern Pacific Ocean around the Equator, which can affect weather around the globe.

The better known El Nino, or the boy, is characterized by unusually warm ocean temperatures in the Equatorial Pacific, according to the US' National Oceanic and Atmospheric Administration.

As the leaders of the rich industrialised countries meet in Germany this week to discuss climate change, among other global concerns, Met Office figures released on Tuesday show the mean global temperature for the period January to April was almost 0.5 degrees celsius above the long term average.

Data from Britain's leading climatologists also show the spring in Britain was the warmest since records began in 1914.

The UK mean spring temperature was 9.0 C, 0.2 degrees above the previos high set in 1945.

The balmy UK spring follows one of the warmest recorded winters, and a run of record breaking years - the last five years are the warmest on record.

The evidence supporting scientists warnings that high levels of carbon dioxide in the atmosphere is warming up the planet is causing increasing public concern.