Journalist Michael Crick has been looking at Conservative Party election expenses from the 2015 general election. In particular, he’s been looking at the vexed question of whether costs related to staff should count against the local constituency expense limit or the much more generous national limit instead:
What stood out for me [in the Conservative national expense returns for the 2015 election] was a series of four bills claimed by the Conservatives for the Royal Harbour Hotel in Ramsgate last spring, in the constituency Nigel Farage was hoping to win, and which saw a fiercely-contested campaign. The hotel bills total £14,213.18 for the five weeks of the short campaign, from 30 March to 7 May.
Yet the legal expense limit in Thanet South for that period was £15,016.38, and according to the Conservatives’ local expense return for the constituency, submitted last June, they spent £14,837 on the campaign, just £179 short of the legal limit. If one included the hefty bills from the national figures for the Royal Ramsgate Hotel – and I suspect many experts would argue they should be – then the total to elect Craig Mackinlay as the MP comes to £29,050, almost twice the legal spending limit in that seat…
Apparently, the Conservatives argue that the staff they had staying at the Royal Harbour also worked in other constituencies as well. That seems improbable, since the nearest other serious marginal seat is about an hour’s drive away. In any case, the Electoral Commission rules make it clear that if an expense covers more than one seat then the cost should be apportioned between the local accounts for the various places… 
The Electoral Commission has [now] asked the Conservative Party to explain why the party decided four bills for a hotel in Ramsgate during the general election should be attributed to national spending. 
There are three, closely-related issues here.
One is the way in which the national expense limits allow local limits to be circumvented (on which see Constituency expense limits are dying off in the UK, but neither politicians nor the regulator will act).
The second is how the exclusion of the direct costs of most staff from national expense limits encourages a staff-heavy approach to political campaigning. (My favourite memory of talking to the Electoral Commission when I worked at Lib Dem HQ dealing with such matters related to just this. I was checking with them if they agreed that the rules as passed by Parliament meant the salary of the General Election Planning Manager did not count against the general election expense limit. They agreed.)
The third is that the question of staff costs for constituency limits has always been rather dodged by the Electoral Commission – nominally referencing taking a stern line in interpreting the law but never acting on it. Indeed, past Electoral Commission reports into general elections in many ways gave the green light to parties to take a very permissive view on what staff costs have to count against constituency limits given the sorts of activity those reports mention without any action, censure or even expression of unease.