Better weather in May or October?

Every season is rainy in England ;-)

Statistically the rainiest months are October and November though....

May has quite a bit more daylight than October - 15 to 16 hours as opposed to 9-11 hours in October.

http://uk.weather.com/climate/sunRiseSunSet/London+GLA+United+Kingdom+UKXX0085:1:UK?month=5
http://uk.weather.com/climate/sunRiseSunSet/London+GLA+United+Kingdom+UKXX0085:1:UK?month=10

I would go when is best for you both could be nice and sunny both could be very wet. As above October historically has the wetter weather but these days who knows. There are school holidays in both months and May has two bank holidays which push prices up.

spring or autumn

Spring is the nicest and driest time of year in Britain. But it rains all year, dull damp patches occur, so you can always be unlucky and have a wet or dull week. There's something to be said for going in autumn: you know it is going to be wet, and you can be pleasantly surprised if it isn't; whereas a wet/cold/dull week in spring is disappointing.

You've got a better chance of good weather in May but don't stress about it - the national pastime is complaining about the weather (despite it being some of the best weather in the world, with no extremes and good for farming)

If you think 330 days a year of grey skies is the best weather in the world,then I agree........

'Good for farming' is not of great use for the average tourist I would suggest.

"Better weather in May or October?"

If we could answer that accurately, we'd all be lottery winners. :-)

Lucapal - where do you get your 330 days a year of grey skies from? Not sure I agree. I did a quick google and found that someone in Manchester recorded his days of rain in 2013 and it was under 200 - 53% of the weather was rainy that year. London is a lot drier than Manchester, though perhaps you literally meant grey skies and not necessarily precipitation. According to the weather people next year and the year after are likely to be warmer than usual.

Not sure about the accuracy of 330 days but I must admit that sometimes you can get a whole week or more of cloud without any rain at all, one of the downsides of living in the UK (weather wise that is).
With the promise of warmer weather next year, doesn't really mean it will be less cloudy.