If you believe that Sterling will fall against a particular foreign currency, or against foreign currencies in general, you might want to look for an ETF that is long the foreign currency and short Sterling. For example: GBAU (short Sterling / long Australian Dollar) or GBCH (long the Swiss Franc and short Sterling). I personally know that these exist but have not read up on them so very much DYOR.
Alternatively you can buy shares in foreign companies on foreign exchanges through one of the many brokers that offer the facility. Selftrade is the one I use. If foreign exchanges and all the tax red tape are off putting then invest in the international section of the London Stock Exchange to buy, say, IBM or Novartis. Or buy British based exporters. Most annual reports indicate the percentage of overseas sales. Alternatively you can invest in foreign domiciled companies that are quoted in London either on the main market or on AIM.
You can find out about the last - which is probably the easiest route - here:
International Companies on the London Stock ExchangeThe LSE site has a great deal more interesting information such as Landmark which lists UK companies by region / country. You can look up local companies of which you might have personal knowledge.
On the Sterling issue, I am agnostic. Most governments are run by criminal lunatics and moral bankrupts. So I just try to avoid investing in areas most vulnerable to political sabotage. I have a personal list of countries so bad (morality or economics) that I will not invest in them. In the long run I think that those two factors become one and the same.
Being British, I still invest here despite the decades long degeneracy of our politicians and electorate. I just avoid construction and industries where the government (national or local) sets the prices.