Really? I wouldn't have thought that 4 schools is too many for a graduate program. I applied to about 4 for my master's degree, and my husband applied to about 5 for his PhD program.
4 or 5 are okay, but the OP says they are applying to 10 universities, including the 4 mentioned - which I have to agree seems quite a lot, especially when you consider that students are only permitted to apply to up to 6 universities with UCAS for undergrad study. It may also come across that the OP is unsure about what they want to do and perhaps hasn't put enough research into how each course will meet their specific needs.
It's difficult to say anything about the competitiveness of getting onto UK postgraduate courses - every course and every university is different. I'd recommend perhaps emailing or phoning the departments in the universities and asking for some information about the course. It's really going to depend on how many places are available, how many people have applied/are applying to start on the course that year, etc. Some universities are much easier to get into for postgrad study than for undergrad study (i.e. a student might have a better chance of getting into Oxford or Cambridge as a postgrad rather than an undergrad) and others can be harder.
Last year, I applied to 3 universities for postgrad study - Bristol, UCL and Leeds - and I was offered a place on each course, so it was up to me to pick and choose which one to take. I turned down UCL right away because the fees and living costs were too expensive (£5,000 home fees plus they recommended having £11,000 in living costs). I also turned down Bristol, but since the letter from Leeds stated that the course would not run if there were not enough students enrolled, I asked Bristol if it would be possible to attend if the Leeds course did not run. However, in June of last year, I realised I wasn't comfortable about going to Leeds, so I went to meet the course tutor at Bristol, loved the department and went there instead.
The applications were fairly simple, including CV and personal statement and a list of the other universities I was applying to, but I did not have interviews for any of the courses. I was offered a place at each in January 2006 and then after I'd accepted, I was invited for an interview at Leeds for scholarship opportunities. With Bristol, I called them in mid-June 2006, stating that I might like to attend Bristol instead and was invited to come and meet the tutor and see the department before I made my decision (not really an interview though as the place was mine if I wanted it).
In terms of competitiveness, I didn't feel there was much for any of the courses in my subject area (Geophysical hazards/Earth Science) - the course at Bristol has a different intake each year - 7 students in 2005, 14 students in 2006, 19 students in 2007, so I think places are offered to most applicants, including both UK/EU and foreign citizens (there have been students from Belgium, Italy, Chile, Africa, Asia etc.).
A few months ago, while at Bristol, I applied for a PhD program in the US (at the same US university I studied abroad at in 2003/04) and was offered a place on the program with no problem. It was the only US university I applied to because I had contacts at the university and would just be another face in the crowd if I applied to any others (my supervisor suggested I apply to Harvard, MIT, Berkley etc. but the applications were very long, I couldn't afford the application fees and I knew there would be a lot of competition). I thought it would be better to apply to a university I knew I liked and was likely to get into rather than putting myself through the stress of applying to the other universities and then getting rejected (i.e. the MIT application was 10 pages long and required me to list every single class I'd ever taken and which textbooks had been assigned to each class, whereas the application for the other uni was just 1 page long!).