Actually its not as simple as saying that sterling is weak or strong (and for the record, yes it is currently very weak against the euro (fact) and may get weaker (speculation), so the title of the thread is not very good).
The bottom line is that you are thinking of going to a major UK city to earn and save as much as possible (I think).
As someone who has been there, I can tell you the following:
1. London can be expensive if you are not careful, rent and entertainment can cost you loads, the sky is the limit. But the same can be said for Dublin. I would say that for the same lifestyle in Dublin and London you will pay the same in euro equivalent. And if you are smart and want to save, you can cut right back on those anyway. You will prob have to budget some for flights and calls home, not huge tho.
2. Salaries are higher in London. Whoever said they are higher in Ireland - get a grip!! Opportunities are much better in terms of CV. Even allowing for the current weak pound you will be earning more.
3. So you should save more. At the end of the day you should have more euro in the bank than if you stay in Ireland.
4. Use a good moneychange service e.g. moneycorp.com or many others. Consider sending money back regularly to hedge against further sterling deterioration. If you want to gamble, wait and hope it goes back up! Up to you. I fed my cash back at regular 6 month or so intervals when the rate was good. I got a lot back at around 1.50, and i'd say on average I got about 1.47 or more. Keep any eye on the rate.
5. If you buy a place, remember you might suffer a poor rate when you go to sell and bring back equity. I am prob going to suffer from this. However, I hedged against this by releasing as much equity as possible, moving it back at a good rate, and going interest only on my place which is now let out to cover the mortgage. May not apply to you.
6. I think 2 years is the minimum to make this worthwhile unless you are contracting or something. You may end up staying longer than you plan tho ;-)
I think you know what you are doing even tho the title of your thread is wrong ;-)
Go for it.