Debt/Credit ratio

Hello

I have recently started clearing debts and focusing on my credit file in anticipation of a long mortgage fix when my current deal expires in December.

As of August my debts will be;

MBNA credit card - Balance - £4100, 0% interest until 07/2020 (£7,700 limit)
PCP car loan - Balance - £13000, 0% interest for term
Couch loan - Balance - 1000, 0% interest for term

I also have a Tescobank CC with a £6600 limit that I no long use or need.

A next directory account with a £6000 limit which is paid off in full whenever I make a purchase. I only keep this on as 4 times a year they have a 'VIP' sale where I pretty much restock my wardrobe for half the price, before the public can shop the sale. Closing this facility would actually cost me a significant amount of money as they also sell designer brands on the sale which are also half price.

The reason I am posting is to ask what the best course of action would be in terms of the unused available credit. Should I close these accounts or reduce the available limit? What are the implications of these options of my credit file?

Thanks in advance!