Very confused and needing advice. I currently have a claude butler racer, with 700x32 tyres, that i use to and from work along roads and towpaths which are not in the best condition. As i live in london this means i come across many potholes but the racer deals with everything thrown at it. On these daily journeys I carry work clothes and lunch in a rucksack. I also have a MTB with larger tyres that i use to transport the kids around on a child seat usually at the weekends. Now here is my problem: What bike that combines these requirments should i go for? Due to a lack of space i need to have one bike for both these purposes. I want a bike not too heavy that i am competely knackered by the time i get to work but also not so light i can't put a child seat on the back. My budget will stretch to £500. Any suggestions?