Why aren’t staff costs included in a political party’s national campaign costs?

One of the key contested areas in assessing an election expenses claim, is how much falls under the national spending limit and how much is local. However there is also a very large loophole in the national spending limit.  It does not include staff costs. If a party appointed someone as a General Election campaign co-ordinator, based at party HQ, that person’s salary does not count towards the national spending limit.

When the last government legislated to limit the amount that charities and campaigners can spend in elections, staff costs were explicitly included in the spending limit. So if a registered third party appoints a General Election campaign co-ordinator, their salary would be counted.

Why are political parties allowed to keep this loophole?