Shares in RBS (LSE: RBS) have risen by as much as 8% today after Brexit fears eased. Opinion polls released in recent days have shown a rise in support for Remain and it now appears that while the referendum will be very close, Britain should stay in the EU.

Clearly, this would cause investor sentiment to improve in the short run and evidence of this can be seen in the FTSE 100’s rise of 2% today at the time of writing.

As a bank that’s UK-focused and therefore highly dependent on the performance of the UK economy, a vote to remain should be good news for RBS’s share price. That’s not necessarily because a vote to stay in the EU would be better in the long run for the UK economy, but rather because it would mean less uncertainty in the short run. And with investors being averse to uncertainty, share prices for UK-focused companies such as RBS could benefit.

With RBS having a forward price-to-earnings (P/E) ratio of just 10.9, it appears to offer a relatively wide margin of safety. As such, and while its shares are likely to be volatile in the short run, it seems to be a sound buy for long-term investors.

Room for more gains

Also rising today are shares in convenience store operator McColl’s (LSE: MCLS). It’s up by around 6% despite no significant news flow being released by the business. As with RBS, a surge in support for the Remain campaign is most likely responsible for McColl’s rising share price and with the company’s valuation being exceptionally low, further gains could lie ahead over the medium-to-long term.

For example, McColl’s trades on a P/E ratio of just 8.7 and while the company’s bottom line is due to fall by 2% this year, it’s expected to return to positive earnings growth next year. Such a low valuation indicates an upward rerating is on the cards and even if that takes some time to be achieved, McColl’s has a top-notch dividend to keep its investors’ returns ticking over in the meantime.

In fact, McColl’s currently yields a whopping 7.6% from a dividend that’s covered 1.5 times by profit. While dividend growth may be somewhat lacklustre over the medium term, such a high yield has huge appeal for income-seeking investors.

Shares take a tumble

Meanwhile, shares in Circassia Pharmaceuticals (LSE: CIR) have tumbled by around 58% today after it released disappointing results from a phase III cat allergy study. Circassia found that there was little difference in the results between its treatment and a placebo, which it says is both surprising and disappointing.

With there being high hopes among investors for the potential treatment, it’s of little wonder that the company’s shares have fallen so heavily today. And in the short run at least, there could be further for them to fall.

Of course, Circassia will now review the full dataset and focus on its broader potential as a business. And in the long run, the company has the potential to make a strong comeback. However, while its shares are so volatile, it may be prudent to invest elsewhere.

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Peter Stephens owns shares of Royal Bank of Scotland Group. The Motley Fool UK has no position in any of the shares mentioned. We Fools don't all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors.