Hi Chris, welcome to the forum
Surprised no-one has answered this yet. Anyway...
A smart camera bag is relatively tough. What about something like the
Crumpler New Delhi 510? The list price is pretty expensive, but then all Crumpler stuff has a high RRP and you can usually get it much cheaper. According to Crumpler it holds an SLR, 3 lenses/accessories and a laptop up to 33x23x3cm. It's leather and relatively smart. It comes in 2 larger sizes as well if needs be...
There are a lot more bags which fit your second requirements (apart from the removeable section but it's still possible). Personally, I use a
Kata DR465 which I use for hand luggage. The top section isn't huge but has enough room for a single change of lightweight clothes. The bottom camera section can be removed so you get the whole of the bottom of the bag as well (there is still the divide between the 2 sections though).
There are also things like the
Crumpler Muffin Top Half Photo,
Crumpler Messenger Boy Half Photo or the
Lowepro Versapack Range.
I think I've got through more bags than anything else... In case it helps to work out what you can fit in what, I use a Kata as mentioned above and a
Crumpler Muffin Top 7500 which they don't make any more (hence the link to pictures on another forum). I can fit ALL my kit in both bags and that consists of a Nikon D90 with grip attached, 10-20mm, 18-105mm, 70-300mm, 35mm and 85mm lenses and a couple of filters, spare cards etc. I'm always amazed it all fits in either bag but it does...