England and Wales have had the driest January since 1997 and the sixth driest on record, the Met Office says.
South East England has suffered from a drought from 15 months
Some parts of the UK have had less than a quarter of their average rainfall so far this year.
In total England and Wales had just over 33mm of rain during the month - a drop of 37% on the long-term average.
If dry conditions continued, South East and Central Southern England could see the worst summer drought in 30 years, Environment minister Lord Bach said.
Those areas have suffered a drought since November 2004, as 13 out of the past 15 months have recorded below 1961-1990 average rainfall.
The worst affected areas were Hampshire, Sussex, Surrey, Middlesex and Kent, which have received around 70% of their normal rainfall.
The Met Office also said that 2005 in South East and Central Southern England was the 4th driest on record and the driest year since 1973.
"Across much of South East England, this summer may be the worst drought since 1976," Lord Bachs told peers.
Many peers backed a call from Labour's Lord Borrie for compulsory water metering to tackle Britain's long-term problem of water shortages.
Other dry statistics for January included:
- The Midlands and East Anglia had only 31% of their average monthly rainfall - 22.4mm and 15.7mm respectively
- South East and Central Southern England had 24.8mm of rain, 32% of the long-term average
- South West England and Southern Wales had 44.5mm, 33% of the long-term average
- Eastern and North East England had 29.4mm, 42% of the long-term average.
The Environment Agency had earlier warned that water restrictions could be imposed if dry conditions continued into spring and summer.
Hosepipe and sprinkler bans, more drought permits and drought orders to help water companies manage supplies may be needed, she added.