According to Official Guinness Records,
The largest trousers measured 12.19 m long (40 ft), with a 7.92 m waist (26 ft), were made by Rishi S. Thobhani from R.S.T. International Limited (UK) and displayed and measured in Leicester, UK, on 23 May 2009.
The trousers were thermal long johns.
For a complete list of 2009 records, please visit 2009 Guinness Records in United Kingdom.