I was at a market in Northern France a couple of weeks ago, and let me tell you, there is no way any vehicle attack was getting anywhere near either of two huge adjacent market places. There were concrete barriers on nearly all access points, and the others, which were emergency access routes (as this attack exploited), were covered by movable barriers which are capable of stopping a truck, and all manned by groups of four armed police or military.
I don't know about Broadgate, but there will be *some* measures in place. At Warwick Uni, the potential "crowded spaces" are designed in consultation with Counter-Terrorism police to reduce the possibility/impact of vehicle attacks. It's all very subtle but very effective, i understand.