I'd seriously give Charles Tyrwhitt a go, they have massively increased their range of "business casual" over the last few years.
personally I would go for stretch fitted chinos, pleated ones are a bit 60 year old man IMO!
Shoes, herring yes but also look at the Northampton factory outlets, had some cracking bargains from Barker directly:
Barker shoes are an English Shoemaker that has been producing handmade shoes using traditional shoemaking methods since 1880. Popular styles including Brogues, Oxfords, Derbys, Loafers and Boots.
www.barkershoesoutlet.com
Also, maybe wait until you start to see what the actual dress in the office is, at my office (City law firm with a similar dress code), the norm these days is chinos, shirt (mix of normal and button down), but paired with smart-ish trainers rather than shoes