Surely this was simply a case of failing to plan for a suitable exit off the RW, especially with traffic close behind or traffic waiting to line up. If you're not sure of what exit to go for, ask the TWR before landing. If you miss your exit at LHR, where they have only a minimum 2.5 mile spacing, you will most probably cause a GA. This is all to do with situational awareness. I am very aware of said 738's on my 6 going into STN too. You see them in bold on the TCAS!