Fall travel in UK

Regarding travel clothes, that's an entirely personal issue depending on what your preference is... some like synthetic clothing, some don't. I like cotton poly blends personally as they shed wrinkles quite well, and dry much quicker than pure cotton. Ideal if you're traveling light and washing your own clothes along the way...
England in Sept, from my experience, is mild weather( lightweight short or long sleeve top with a light jacket/sweater will suffice ) but be prepared for rain...not everyday but you should expect some rain while there

We were in England and Scotland in late Sept/early Oct last fall and it was fairly cool. Plan to wear layers and take a warm (not heavy wool) jacket. Turtle necks are good as well as a rain jacket.

Two years ago I was in ice and sleet from Snowdonia to almost London and picked it up again the next day from Paris to Limoges. This was mid-September to early October. Last year at about the same time, I switched from shorts to a wool cap, jeans, and a double jacket and had to knock ice off the mooring ropes to get going on the midland canals. The Brits don't have their weather very well organized. Until they do, bring layers.

Layers and Rainwear! The saying goes " In the UK if you don't like the weather just wait 5 minutes". It could rain, could be sunny, could be cool, it could be all that in a few hours. I've been in the UK in every month but December and January. Winters aren't as drastic as in the States, summers aren't quite as hot and humid. It's a big island and the weather can move through fast. September should be fair weather. I have been there in late spring and summer when it was fairly cool sweater (jumper) weather.

I go for multiple light layers in non-cotton fabric. When cotton gets wet it loses all insulation, plus tends to stretch and lose shape if not machine dried. A lightweight washable wool sweater makes a perfect layer. For England in September I would pack either two light sweaters or a sweater and a 100 weight (lightest weight) full zip fleece. If it gets really cool you can wear both with a t-shirt, or two, underneath. Always have a good waterproof (and preferably windproof) hooded rainshell, that's long enough to cover your bottom, handy. A day may be beautiful in the morning but pouring rain after lunch.

Will the weather in England the last of September be too cool With the greatest of respect, who knows? I certainly don't. I've been here for years and every year is an adventure. September can be warm, cold, freezing, hot, wet, dry, or many or most of those in one day or week. I haven't seen snow in September yet - saw it in late June once though.

I'm going to join the layers crowd. For me, the trick to comfortable travel in the UK (primarily Scotland) has been to have a good rain jacket that is water proof, not water resistant and has a hood. That way I don't have to balance an umbrella with my camera. I always take a light weight fleeces - summer, spring and fall and then buy a new sweater in Scotland. I take some long sleeve and short sleeve tops. The first time I went, which was in early September, I took silk long underwear. I never needed it. But, it you're worried, that's one way to add another layer. My mom swore by her lined jeans from LL Bean. ; ) Pam