Coast to Coast Walk - best time of year?

Hi all. Thinking of doing the St Bees to Robin Hoods Bay walk across Northern England.

I know the weather is never reliable & it can rain & rain & rain, but is there a time of year when this is less likely?

I did the walk once before in Sept '98 & we had a couple of days of rain (not too bad), but talked to others who had been thoroughly rained-out in June. Was I lucky or is Sept as good as it gets?

British weather is notoriously variable.
However, by walking west to east (St Bees Head to Robin Hood direction) you are more likely to have your back to the prevailing wind from the west (and whatever rain it may bring).
Walking in June means longest daylight hours, which can help eg if it rains early in the day, you can set off later and still be OK walking at, say 9pm. However, that might not suit accommodation and pub meal hours.
Both June and September are outside all UK school holidays, so equal on that score.

Finally, there's no such thing as bad weather, just the wrong clothes.

That is the beauty! of the UK you never can tell the last couple of years end of April early May has seen the best weather for the whole summer. You just have be prepared for all seasons no matter when you come.

Average rainfall stats, taking into consideration acceptable temps too and tourist numbers - with all the caveats - late spring & early summer ideally avoiding spring break week focused around England's Spring Bank Holiday Monday weekend (last Monday in May).

Thanks for the advice.

The C2C will be part of a six week break & I expect we will allow three weeks to do the walk. We will have our (then) 10 year old daughter in tow, so will be planning to include Australian school hols in our travels to minimise time out of school.

So working around school hols, we have these options for the C2C:

Early-mid June (return to OZ after June / July school hols).
Early-mid Sept (return to OZ after Sept / Oct school hols).

From the advice above, it sounds like the June option is preferred. This would give us longer daylight hours & less chance of rain (no guarantees). Have I got this right?

That's about it - yep. But as you have grasped, England, particularly its north & west, is very much of the maritime variety and reliance on averages can only be a very broad guide.

Understood. We were in Sheffield mid-late June 2012 and it rained and rained and rained (which stopped us getting out into the Derbyshire Moors unfortunately).

So I guess we know how bad in can be. Hopefully, wet Junes isn't a new trend.

Was I lucky or is Sept as good as it gets

It depends exactly when in September. September is on average a wet month, but there is often a dry spell in early September. June is on average a dry month, but there is often a wet patch. March-May is the driest three-month slot of the year, but Mar-Apr is a bit of a risk because its still cold with risk of snow in the hills. And of course it can rain any time.

What actually happens in any given year is very sensitive to where the jet-stream ends up that year. Summers tend to be either wet or dry depending upon where the jet stream sets itself up for the period. And this can vary by how far north you are in the country - the south can have a wet summer and the north a dry one, and vice versa.

Because the jet stream does move to the south in the winter, there is a tendency to have a wet patch in late spring or early summer as it heads north (often in June - sometimes coming a bit late and disrupting Wimbledon), and then to have a dry patch in late summer or early autumn (often in early Sept) as it heads south and brings in the rains of autumn. But the thoroughly rained out June we had last year was because the jet stream was in quite an unaccustomed config altogether.