I am an indian national, currently staying in USA. My current H1B Visa has expired and I am planning to travel back to india via London, UK.
Will I require an airside transit Visa for London?
Yes, you will need a visa to transit through London in your case
Firstly, you can use the UK Border Agency Do I Need A Visa tool to check if you would normally need one. That comes back with
Next, you want to look up the 'Transit without visa' concession - DATV exemptions (you'll have to click to expand the section). From there:
As your visa will have expired, it will not count as a valid entry visa for the USA, so you won't qualify for the 'Transit without visa' concession. Thus, you'll need to apply for a Transit Visa. Well, either that, or leave the US before your current visa expires!