I personally believe all teams who reach the SF have equal chances of reaching the final, it will come down to who handles the pressure much better; BD are inexperienced on such a high profile stage but deserve as much respect as the other teams. If Pakistan find themselves in such a situation their confidence will be sky high, historically we've done fairly well:
1992
1999
2009 CT and World T20
2010
2011
Out of 6 Semi-Finals we've have succeeded in 50% of them so there is no real mental block.
England are a beastly team but they are not invincible:
http://www.espncricinfo.com/ci/engine/current/match/913661.html
Even with a weaker XI we managed to do a job on a full strength England XI, they are due a loss and it remains to be seen how they cope with the pressure of a high profile game in their backyard. England for me are boxing equivalent's of a fighter who is "chinny" this can be concealed when you're very sound technically but a vulnerability does exist and it will only take one moment for you to fall. I actually would be more excited to face England in a Semi-Final then any other team.
Anyhow we need to take care of Lanka first and they are very dangerous in their own right, I see them as the tougher opponents then England although it's understandable for people not to agree with me in that regard when it comes to looking at both teams on paper but cricket can be a funny game, momentum and mentality are everything.