It isn't difficult if you have the correct documents, and evidence that you plan to return home...such as a letter from your employer, and proof that you are able to finance your trip. Also, you will need either a private invitation, or confirmation of a hotel booking. This is not only because of terrorism, but to prevent people from staying when their visit ends. Britain is struggling with both legal and illegal immigration problems, but it is still possible to visit and emigrate here for genuine reasons.