After a long time faffing about with light/heavy/showerproof/windproof/lined trousers I bought a pair of Paramo Cascadas' - £80 but one pair is all you need - wind & water proof, insulating.
I wore mine for most of the summer too - they have full length side vents.
I don't have to think what the weather is (or likely to be) - you won't win a fashion prize wearing them you'll be prepared for anything.
My winter attire is Cascada trousers, Torres smock and Explorer top.
Ancillaries - Buffalo mitts, Buff, Millets 'charcoal' handwarmer, Paramo balaclava, Millets gaiters, Karrimor KSB goretex boots.
Trousers
Smock
Explorer top
Balaclava
Buffalo mitts
I fell into the trap of 'I'm only a birder' what do I want with fancy South American mountaineering gear - I'll just get some cheap stuff.
I ended up with cupboards full of 'bargains' as I extended my range and willingness to get out in any weather - choosing what to wear was a nightmare.
I gave in and bought Paramo mostly at bargain prices offseason, also use their underwear, shirts and T-shirts.
My only concession was to Craghoppers as I particularly like their Atol T-shirts for work and their Merino tops (for warmth) and (mostly because they sold them to me for £13).
Wearing Paramo makes me feel more secure too - as I use a GPS I often stay out after dark in remote places - wearing clothing that does not attract moisture and is inherently warm I wouldn't worry too much if I had to curl up under a hedge for the night.
I therefore 'always' have a plastic bag containing spare - buff, gloves, Merino top, whistle, batteries, compass, Mars bar, Gaffa tape, torch, string, lighter, spare 'charcoal' for handwarmer.