What is the tax treatment for dividends paid on open CFD positions?

If an investor has an open CFD position when the underlying stock goes ex-div, there will be a payment made to the margin account in lieu of dividend. This is to ensure the investor does not actually lose money when the price drops as a result of the company returning capital to investors. What is the tax treatment of this dividend payment in the UK, is it treated the same as normal stock dividends or is it capital gains?