He told the Liberal Democrat conference this would ensure 350,000 top earners paid their “fair share” of tax, the BBC reports.
Alexander said a crackdown on tax evasion and avoidance announced a year ago was working, with £2bn set to be raised this year with a target of £7bn by 2015.
There already exists a special unit within the Inland Revenue to focus on the tax arrangements of the wealthiest 5,000 people in the UK.
But the new staff will be employed to scrutinise the accounts of an additional 350,000 people who each have a total wealth of more than £2.5m.
Alexander said: “It took 12 years for the previous government to take action against the wealthiest 5,000 people, some of who weren’t paying their fair share of tax.
“We can do better than that.
“My message to the small minority who don’t pay what they owe is simple. I agree with the chancellor. We will find you and your money and you will pay your fair share.”
