I should not disclose medical issues/tests when applying to life insurance – it will mean a higher premium.

While this may be true, if you do not truthfully answer all questions at application, particularly on your medical status, it means there is a good chance that any claim you make on the policy will be declined due to incorrect information provided initially. If you are more likely to become ill or die, then your premium will be higher, but by not disclosing all facts at the outset you risk the cover needed to protect your family if the worst happens to you.