The facts are that currently the UK is required to pay  just over £350m per week, but due to a rebate, the actual figure paid is around £250m

That much is correct.

However, the rebate is negotiable and not part of any treaty whereas the the level of our gross contributions we pay to the EU is set.  Thus, the rebate is open to being reduced or removed at any point and what is already known (as this is set in the pipeline) is that by 2020 our contributions will increase (due to more poorer countries joining) and the rebate will have to be renegotiated, if it's still available.

We then receive some of what we contribute back for such things as farming subsidies, regional developments etc, but overall I think that this is around less than half of our net contribution.

It goes on giving other countries subsidies and grants for development in order to theoritically increase trading areas and regional stability, as well as giving a few very rich and powerful bureaucratic eejits unknown sums and expenses.

That's the nice idea - but the other reality is that the UK is a net importer of EU goods, so taking that into consideration, there is a hidden amount of wealth going to other EU countries who sell us their goods.