If you live in Canada, you need your Canadian passport to return to Canada and there is no question you will need that passport, so I am assuming you want to know if carrying your "asian" passport is necessary/required/convenient. Canada does not have missions everywhere and if you need any type of help abroad, it is always a good thing to have all the help you can get from another consular mission. However, of course, if you needed help to get repatriated to Canada, an "asian" mission may not be able to help you. My advice is that you carry both if you feel your "asian" passport will get you the help you might need should the Canadian mission fail. Also consider the risk of losing your passports; how easy it is to get a new passport from your "asian" country is something to think about. London has an actual government mission, but in Belfast, Edinburgh and Wales consular services are provided through honorary consuls, which are not employees of the government of Canada, but rather 3rd party employees, yet, this is not useful because services are provided in London. You may want to check the missions of your "asian" country in the UK and decide whether carrying that passport is a good idea.