I mean based on your descriptions of the courses it sounds like you already know? If the UToronto course is more industry aligned that's probably less suited to your aims of pursuing a PhD in the first instance. And if the UCL course is less suited to developing your background as you want/need for the PhD project(s) you may be interested in doing, then it seems Warwick is the natural fit.
UCL is also somewhat just "OK" for both maths and CS anyway I'd note. It gets a big "bump" in perception due to being in London in those areas and there are plenty of other stronger courses in those areas generally. Warwick specifically is in an entirely different league to UCL for maths by most accounts. It's also very well regarded for CS and its business school, so seems to tick all the boxes.
Obviously do consider that Warwick is a campus uni in a suburb of Coventry so a very different experience to living in London (albeit, undoubtedly cheaper cost of living - no idea how tuition fees compared though). This may or may not be a big deal for you (although Warwick is a target university for investment banks in the UK so routinely has city firms hosting careers and networking events there, so at least that should not be a worry).