Britain’s benchmark FTSE 100 index could fall to its lowest point since 2011, slipping below the 5000 mark if the country votes to leave the EU, according to UBS.

In a note titled “A roadmap for the ‘Day After’”, strategists at the Swiss bank calculate the FTSE 100 could suffer a more than 20 per cent decline, falling to 4,900 in its worst case scenario (see table above). The FTSE currently stands at 6242. UBS’s calculations do not specify a time period for the moves.

“Following the risk rally of the last few days, we believe there is significant room for downside in the event of a ‘Leave’ vote,” wrote Yianos Kontopoulos at UBS.

The pound would also come under “significant pressure” with haven currencies such as the Swiss franc and Japanese yen seeing inflows in the days after Brexit, said UBS. It estimates the euro could appreciate by as much as 17 per cent against sterling to €0.90 against the pound.

Calculations from SEB predict the pound could fall as low as $1.289 against the dollar in the event of a leave vote – around a 30-year low.

Of course, those two things could, eventually at least, cancel each other out. Analysis from strategists at Deutsche Bank suggests UK equities will manage to outperform their European peers after a Brexit, on the back of a falling pound.

The Swiss bank forecasts the Euro Stoxx 50 index could be in line for a 23 per cent decline, outstripping that of the S&P 500 at -9 per cent at the near 20 per cent drop pencilled in for the FTSE.