I'm not an expert in the area, but I think the lack of disclosure would void your existing cover. It would come to light if a claim was made, and insurer wouldn't pay.
That aside, the legislation requiring mortgage protection is actually to protect you, not the bank. If you can show you've been refused cover then the bank can waive the requirement. They all have their own underwriting policies so you would need to ask (or use a broker who's familiar with all the banks policies).
There are a few insurers specialising in this type of cover, but it's expensive. Most are UK based, so they might be scaling back on writing new business here.