LONDON, May 23 (Reuters) - The British government is not ruling out a windfall tax on oil and gas companies if the companies do not invest their profits in boosting capacity, Chief Secretary to the Treasury Simon Clarke said on Monday.

Asked about the possibility of such a tax, Clarke told Sky News: "We are certainly not ruling it out."

"We recognise there are extraordinary pressures on family finances, and the industry needs to hear the message loud and clear. If investment doesn't go in, we can't rule (it) out." (Reporting by Kylie MacLellan and Farouq Suleiman, Editing by Paul Sandle)