Immigrationboards.com

Would the HO inform the country of origin that one of their subjects is now a British one?
I would like to keep my original passport (which is of a country that doesn't allow dual/multiple citizenship) as it allows me visa free travel in a number of countries where a British passport doesn't.
Anyone with experience on this?

The HO doesn't let foreign governments know you are British. It is a matter between you and that country. I assume you are aware that what you are doing is illegal and could have consequences if you are caught with a passport that is not valid anymore (as you are not a citizen).