If you hold onto a bno passport then you can enter the uk for 6 months without the need for a visa.
Request an nzeta (new zealand electronic travel authority). The listing is from the older british government website which no long holds any bno information. Visitors who want to visit vietnam during tet can apply for tourist visa with higher fee than usual. If you hold onto a bno passport then you can enter the uk for 6 months without the need for a visa.