Why are you assuming a single income? That's not realistic.
Extra living costs, taking food for example. 2 people can take advantage more of special offers on fresh food.
Assuming an equal division of labour, this can make bulk cooking more economic.
More water and energy are used, sure.
It's possible more heating is used, if one party is in whilst the other out. However, arguably offset as both are sharing the bill and likely to both be home when heating is used more than not.
Don't know about the marital tax allowance but Ann's general point stands. i.e it's not really fair to charge single people the same council tax as a household of more than one adult.
There was a report / article fairly recently saying single life is generally more expensive than for a couple. LMGI.
e2a this one will probably do.
People who live alone spend almost twice as much per person as those in couples, research has revealed
www.theguardian.com