只持有英国签证然后免签证去爱尔兰？

理论上可行，具体请咨询大使馆以下for your reference，条文里面并没有要求英国visa必须是在中国申请的，具体还是问下大使馆吧
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The following are exempt from holding a visa:

Passengers with a Hong Kong (SAR China) passport.

Passengers with a Macao (SAR China) passport.

Nationals of China (People's Rep.) with a "Passport for Public Affairs" if accompanying a Minister or a Chinese leader of Ministerial rank or above on an official visit.

Nationals of China (People's Rep.) with a valid C visa issued by the United Kingdom if they have first entered the United Kingdom and been granted a stay of 180 days in the United Kingdom. They are visa exempt for a maximum stay of 90 days in Ireland (Rep.) or until the end of the period of stay granted in the United Kingdom, whichever is shorter.

Passengers arriving in the United Kingdom, including Northern Ireland, and traveling to Ireland (Rep.), the visa waiver programme will apply and only a visa issued by the United Kingdom will be required. The visit to Ireland (Rep.) must be within the stay granted within the United Kingdom.
Passengers are permitted to travel to a third country before traveling to Ireland (Rep.) if the visa issued by United Kingdom is still valid. Furthermore, re-entry into Ireland (Rep.) from a third country is permitted if the visa issued by the United Kingdom is still valid and period of the stay granted in the United Kingdom is still valid. Passengers with a long term visa must visit Ireland (Rep.) within a period of the current stay granted in the United Kingdom.
Passengers arriving first in Ireland (Rep.) and traveling to the United Kingdom, including Northern Ireland, and then returning to Ireland (Rep.) will requre separate visas issued by Ireland (Rep.) and the United Kingdom. However the visa issued by the United Kingdom will be accepted under the visa waiver programme for the return journey to Ireland (Rep.).
Not applicable to C visas issued for the purpose of transit, marriage or to enter into a civil partnership.

Nationals of China (People's Rep.) with a valid C visa endorsed "BIVS" issued by the United Kingdom. They are visa exempt for a maximum stay of:
- 90 days, if the passenger first enters Ireland (Rep.); or
- 90 days or until the end of the period of stay granted in the United Kingdom, whichever is shorter, when the passenger has first entered the United Kingdom.

Passengers who first arrive in the United Kingdom (UK), including Northern Ireland with a BIVS visa issued by the United Kingdom are permitted to:
- travel to a third country, before traveling to Ireland (Rep.) if the visa is still valid; or
- re-enter Ireland (Rep.) from a third country if the UK visa and period of the stay granted in the UK are still valid.
Passengers with long term visas, with the endorsement "BIVS", must visit Ireland (Rep.) within a current period of stay granted in the UK.

Additional information:

Visitors are required to hold proof of sufficient funds to cover their stay.

The following regulations apply to children/minors:

A separate visa is required for children up to/incl. 16 years of age if registered in parent?s passport and traveling accompanied by passport holder.

Important:

Visitors not holding return/onward tickets could be refused entry.

8月亲测可行新加坡办的英国签证，先入境伦敦，后从伦敦飞都柏林。

这是真的吗好想顺带着去一下