I had just the same with my heart monitor. Despite setting it all up carefully I was recording about 180 even jogging! My max for my age at the time (50) should be about 170, so clearly something was up the creek. I felt ok running, but the monitor gave me the impression I was about to have a heart attack. When sprinting I was close to 200, so I just put it down to being faulty and stopped using it.
Shed boy, good luck on that scan, and thanks for your input on my (loose) plan. I'm running tonight then having a break 'till next Wednesday.(friends 50th long weekend party in Peak district) I'm thinking of doing 3 hard weeks and one easy one this time round and see how that works for a while at least?
Howard, good running. I find slow pace on long runs is the way to go. Much less likely to get injured, quicker recovery and a great way of building up stamina at your own pace. I think any speed will come if and when your body is conditioned for long miles.