You’ll need a master’s conversion but you’re also going to need at least a year’s paid clinical experience in the NHS (realistically) and with more than one client group and there are no guarantees. Most people try more than once and some people try for a very long time without getting anywhere.
Bear in mind that a psychology degree is not a vocational degree. It doesn’t qualify you to do much more than your biology degree in principle. If you decide not to go ahead with it or decide to do something else you are going to have to convert again and that gets harder every time. You have to be pretty damn committed and bear in mind that the statistics on people successfully converting to clinical psychology on a conversion degree are ridiculously low. There are plenty of conversion degrees in this country that haven’t turned out a single successful conversion to the clinical doctorate but they continue to market themselves as a route to doing it.
If you’re wanting to do clinical psychology because you want to do therapy, you may want to consider other career options that allow you to do that. The couch, notebook and tissues idea of a CP is not really what the role is all about. You need to consider carefully whether or not you really want to do it or if you like the idea of it more than the reality. Having not yet studied psychology you may find that it isn’t necessarily what you think it is. Have you considered and ruled out other roles that also utilise psychological principles? What would you do if psychology wasn’t an option? If you can’t see yourself in mental health in any role other than a CP, maybe think about why that is.