You cannot enter the UK legally via Ireland if you are a visa national. Ireland and the UK are in a common travel area. Land and sea connections have no border posts. If you fly from Ireland to a UK airport, you will arrive through the same channels as a domestic flight and there will be no border control either (this is not true in the opposite direction but that is irrelevant for you). Moreover, the merest whiff of suspicion by Irish immigration that you might attempt to enter the UK illegally would result in them refusing you entry to Ireland in the first place.

You can fly into a regional UK airport if you wish by connecting from continental Europe with LH, LX, KL, AF, etc... in which case you would go through immigration on arrival in the UK. But don't be under any illusion that it would be any different from entering the UK at LHR.

Either you have a visa that entitles you to enter the UK, in which case they will let you enter, whether it'd be at LHR or elsewhere or you don't and you won't get entry wherever you try to enter from.

If you enter illegally and attempt to work, you run a very high risk of having whatever visa you have cancelled and to be banned from entering the country for many years.