I think 5:1 (5 min run:1 min walk) is a little excessive and will probably do more harm than good IMHO

I have heard of various techniques similar to:

28:2 or
55:5

I have heard Purdey talk of this method when he was doing the Crawley 12 hour and he was pretty well disciplined enough to do it and used the walking breaks to take on board well needed fluids and foods. Knowing you from the Chislet run I know you are quite a disciplined kind of chap.

The few ultras I have done have been trail events so the strategy was quite different to track events where the 28:2 or 55:5 regime can be easily implemented, on trail I approached it with the "Walk the hills, run the flats" and then ensured my food/fluid regimen was much more strictly controlled. My view is 2 minutes wasted on an up hill is 4 minutes saved later on as I needed to keep some energy in the bank. At Compton I found that I was walking just as fast as a person runner and they were just sapping the energy out of their calves.

At the marathon on Saturday my good friend Brian ran the first 13.1 mile loop and power walked the second 13.1 miles....reason, he is training for a 100 mile ultra and was training his legs to take the strain.

Yes it goes against the grain of the seasoned runner, but there are other races to run

Definitely, at the Compton 40 we walked " ever so often" and it really was a godsend and kept the heart rate well down. At some points we were comfortably running 8:15 min/miles which reduced to 9:30 min/miles depending on the terrain.

As an aside but connected I find that rests at checkpoints a real benefit to properly replenish with food/drink, get the legs right the heart rate down and then move on at a run pace.

That's great advice. Thanks.

You're perfectly correct. To enter into a 50+ mile event and expect to run all of it is just going to lead to disappointment. I'm not a talented runner and I'm never going to win events. What I can do is maximum my potential and that means being intelligent about strategy and making sure I've done my research.

I would very much like to plan to walk and have that as a decision already made than crash badly and be forced into a route march.

I think the key thing to get into my head is that I can train all I want, what I cannot do on a very regular basis is test myself at extreme distances. The only way to do that is during an event. I want to get to the end of the events knowing that I completed it in the best time I could, feeling the best that I can.