OK, some thoughts from a slightly different angle.
Most boats separate out into two main painting areas, the hull and the upperworks.
For most commercial or naval vessels Halfords Red Oxide spray is a good match for the underwater part. The topsides of the hull are usually a fairly commopn colour such as black, white or grey. Many other colours can be found in the Halford's range which will often meet the bill. Then you frequently have a band of boot topping which might be white, black or some other primary colour such as green. A good way to deal with this is to use Trimline tape which comes in the main primary colours, has negligible thickness and is waterproof. After you've done all that you have the option of sealing the finish with varnish. If, as Stavros says, Halfords do a semi matt clear finish then that's probably the way to go. That way you will have no compatibility problems.
As far as the upperworks are concerned there is usually a wider variety of colours and in this case maybe Humbrol or Tamiya Acrylics are the way to go as long as you don't mix them. Again, no compatibility problems.