Good question. Don't know about the timing of these lunches, but it seems from the secretly filmed interview that you are looking at a bill of £250,000 if you want access to the PM himself.
Now, in what way is the party in need of funding? What do they do with the money? After all, election expenses , both nationally and locally, are strictly controlled and limited, and backdated to long before the election itself (to stop the governing party spending lots of money before calling a snap election and so gaining an advantage). Is it to pay the wages of party officials?
It does look as though the individual hopes or expects to gain an advantage; indeed the party's own website sets out the levels of donation required for lunch etc with different levels in the party/ government, with the highest level being called Treasurer level. Well, that's fine with, for example, the Royal Academy; the biggest donors get the first viewing at the Summer Exhibition, meets Academicians and get other benefits from the Academy; but it surely has no place in government or party.