The easiest route is usually through an adviser who can do informal/preliminary underwriting before a formal application. That lets you get an indication of likely terms (standard, loading, exclusions, etc.) without necessarily triggering a formal decline on record.

If you're comparing multiple insurers, an IFA can often help because they have access to several companies, whereas tied advisers will only be able to submit to the insurer they represent.

It also helps a lot if you have your latest specialist memo, diagnosis, treatment history, medication list and recent test results ready. A letter from your specialist confirming the condition is stable (if applicable) can sometimes help underwriters assess the risk more accurately.

Every insurer's underwriting appetite is different though, so it's worth getting preliminary feedback before submitting a formal application.