How this will impact the pound? Firstly, as mohdsalleh says, this pact probably won't be too stable. Clegg is a Europhile corporatist who believes in capping banker bonuses at £2,500, hiking taxes, punishing capital, abolishing the UK's nuclear deterrent, and massively increasing immigration, without cutting spending. He is a bit like a Scandinavian politician in terms of outlook and policy. Cameron and the Tories are anti-Europe, they just split from the Sarkozy/Merkel bloc in the EU and aligned with Eurosceptic E Europeans, they want to cut spending and keep nukes, and don't think it's productive to try and crush business or the financial sector. His politics are more mid-Atlantic.
What are the chances of these strange bedfellows lasting 5 years together, let alone passing major unpopular spending cuts without falling out? As for the chance of intelligent financial or regulatory reform - lol. IMO the coalition will show serious cracks within the next few months, a year tops, and probably won't last the full 5 year term. When those cracks appear, the pound will get hit hard.
IMO the pound has major downside here, and only moderate upside. Maybe if the dollar corrects somewhat after its big bull run in the last few months, the pound might get to 1.55, maybe 1.60 at best. But I don't see it going further. Whereas I could easily see it retesting the old lows around 1.35, and in the long-term parity is a clear target. The thing about the pound is that a weak currency would be great for both the Tories and Libs. It would make the UK more competitive in the short-term, lead to more inward investment, exporters picking up business and thus job cuts less needed, profits and tax revenues higher etc. Mervyn King has also practically green-lighted a sterling devaluation. So, you have 5-10 points downside if the pound rallies, which will most likely then revert back as the pound slides again, and your upside is 15 points minimum and quite possibly 40-50 big figures. That is a pretty sweet risk/reward.
Another factor is George Soros's theory on currencies - that the most bullish is fiscal expansion with a hawkish central bank. He saw this in the USA in the early to mid 80s, and again in the early 90s with Germany around reunification. Now, the UK is looking at the EU PIIGS and seeing the problems with lax fiscal policy. It will probably do some kind of cuts at least. At the same time, Mervyn King believes in long-term debt deflation and is sitting with rates at minimal levels for the foreseeable future. So, we have a classic case of the exact opposite of Soros's currency bull market theory - the UK will, for several years, face fiscal contraction combined with an ultra-loose monetary policy. That should be very bearish for the currency.
So, my opinion is be short some pounds here, and ready to double up if it gets to 1.55-1.60. A stop can be placed around 1.65ish. Hold for the long-term. If the pound does reach parity, that is a fat 45-50% return from current prices.