Medium and good developers usually look at well known (at least locally) companies for a job. Small companies are generally known for lower salaries, less expertise and sometimes strange owner or management, so the problem you have is lack of reasons for people to apply.

Advertising on your own web site has a very low reach if you are just a small company; who do you think will look this way? At least post it on some job sites; also post in local community groups, like local Facebook groups, if any, unless you are in a large city where this will not work. You can also use LinkedIn, but I don't know what is the cost in UK.