This from one of my accounts:

Margin changes to your account
On Thursday 23 June, UK voters will decide whether to maintain the United Kingdom’s membership of the EU. In the run-up to this referendum, we may see larger than expected volatility as the financial markets react to the final stages of the political campaigns.

This can result in increased opportunity but also increased risk. As a result, we recommend that you have sufficient margin cover in place at all times and continuously monitor your account to make sure that you don’t get caught out by large changes in the market.

Ahead of the EU referendum, Margin Rates will change temporarily on some of our products: