The personal statement really only matters a lot for oversubscribed courses that already ask for very high grades. This is because there are far more academically qualified people than there are places on the course, and most applicants have much the same grades, so something other than just academic qualifications needs to be used to decide who to offer a place to. The vast majority of economics courses are not like that.
If the DC has already ruled our Oxbridge, LSE and UCL, then they have already ruled out most of the courses that will care a lot about the personal statement. Warwick will care, a few others that ask for very high grades might care. Beyond that, someone applying with grades in hand that are higher than asked for will very probably get an offer.
In terms of the personal statement, it is exactly as @ErrolTheDragon has said, it is a personal statement. A person who is actually interested in economics and who, as a result of this interest, has thought about economics and done things to find out more about it, should be able to write their own personal statement in no time at all. They would need to polish and check it and make some minor refinements, but really even one day should be more than enough time to produce a decent draft because it should at this point be nothing more than organising their thoughts.
Admissions people know that people get varying levels of support for writing their personal statement, just as they have different opportunities for doing different activities. This is why we put so much emphasis on the personal narrative dimension of the PS, on the individual showing their own thought processes. Of course, they could just get someone who is interested in and knowledgable about economics to write the whole statement for them, but unless courses interview applicants there is no way around this.
For very competitive courses, generic personal statements (of the type that might be flagged by UCAS or more broadly) are rarely helpful. For the course I teach on, a UK domiciled student without further maths A Level had around a 25% chance of being made an offer last year. Having a personal statement that reads like hundreds of other personal statements is not going to help you be picked out of the masses for an offer. That is why we say: be interesting.