EY (and other large professional services firms) expect their employees to be mobile unless you are doing some kind of back-office administrative role. This is because their work is where their clients are, not really at their offices. If you are not based in London, you should expect to spend a fair amount of time travelling. Even if you are based in London, you may still end up travelling a lot. I know a number of Edinburgh based people working for EY, KPMG and PWC who spend less than 30% of their time actually in Edinburgh. Travel will likely be greater doing Advisory vs Assurance.