Let's start with some basic information:
https://nationalcareersservice.direct.gov.uk/job-profiles/electrician
Clicking through from that website takes you here:
http://electricalcareers.co.uk/career_option/installation-electrician/
There's an important note of caution there:
"An apprenticeship is the usual entry route into the industry – by doing an apprenticeship you’ll gain the NVQ Level 3 qualification that’s most widely used and recognised by the industry.
[i]Short courses are available, but they tend to be of most use to existing electricians. They are very unlikely to be accepted by an employer if you’re new to the industry[i]"
So, while you shouldn't necessarily give up on your ambition, you need to be realistic: it's going to be tough breaking into the industry if you've not come through an apprenticeship.
If you still want to try, your next step will be to find a college in your area that offers suitable courses. (What's 'suitable' for one person might not be right for someone else; it depends, in part, upon whether you've got enough financial resources to leave full-time employment for a while so that you can embark upon full-time education or whether you can only consider evening classes).
For example, there are various courses available in Bristol
http://www.cityofbristol.ac.uk/courses/construction/electrical-installation/
(Post again, giving us a more accurate indication of where you live, if you need more help searching for courses)