Matt
You've had some good advice here. It could well be worth looking at the bigger picture too. If just one of your customers have asked about carpet cleaning, then you should have plenty of others who haven't got around to it yet

And there's probably others who could easily be sold this service.
As you are involved, I think, with contract office cleaning, then there's a fair chance that you could already have most of the equipment you need for Low Moisture Carpet Cleaning. I know it's a fair drive from Essex, but a visit to the NCCA Hands On Experience I have organised for next Monday in Wolverhampton could well turn out to be the most cost effective investment of time and money you will ever make. It is not uncommon for a two man team to earn more than £700 per day maintaining the carpets you have described. In excess of £1000 per day is not uncommon.
If you are truly interested in the potential to earn serious money, then look here
http://www.cleanitup.co.uk/smf/index.php?topic=24781.0 for further details
Safe and happy cleaning

Ken