No insurance payout for pre-existing medical condition (cancer)

Unfortunately most insurers refuse to insure people with pre-existing medical conditions at all and those that do either:
1. hike their premiums so much that sometimes it's cheaper not having insurance and take the risk particularly if you are travelling in some EU countries.
2. specifically exclude anything related to that condition at all (and knowing how insurance companies work if you claim for medical reasons they would try and relate it to that condition.)

I only know this because I had to research insurance for a relative that has a medical condition that sometime affects him.

To be frank I don't think Natwest will pay out for either of your parents because in your dad's case his trip was cancelled because of your mum, who they are refusing to pay out for. If you have the time and energy you could try and argue with them but as your dad knew your mum was receiving treatment it would be quite hard.

There was a recent report on the bbc website about this however I can't find that link but have found this from cancer research- http://www.cancerhelp.org.uk/help/default.asp?page=4343

Under the new t+cs of the Ad Gold that were brought in for holidays booked on or after the 23rd April 2007, if your mother had prescribed medication for her condition, she would not be covered for it, assuming that she's under the age of 70 and had informed of her condition. However, a leaflet and new policy booklet were sent to all Ad Gold customers during March 07 regarding the new changes to t+cs.

But in any case if it was undeclared, there's no cover. There is also the case regarding being aware of an illness of an immediate relative at the time of booking the trip, where cancellation claims will not be paid out.
For AD Gold, the pre existing med questions are based at the time of booking the trip, and the questions as posted as statements in new policy wordings.

Also, stating that the Dr changed her medication won't help as questions will be asked WHY (s)he changed the medication - risk that could be made sick or have a reaction to the medication which can often to lead to further diagnoisis of new condition/new ailment crops up because of the change in treatment..........

Claims can check up on files on the customer service department, as can emergency assistance to see whether customers have previously informed of a pre existing medical condition. Claims are looked at on a case by case basis, on an individual basis, so there could be a chance to appeal the claim.