To be fair, although you have two cards, neither have any "lending" on them, the scoring will be based on what you are trusted with and have the "means" to pay.
Two instances:
1 - You have two cards, both with £2k limit on each, but with no balances due. You will be trusted by the card companies to the sum of £4k in total. Your scoring will be based on how much you paid back previously, and the overall conduct of the accounts.
2 - Two cards again, this time with £10k on each. Whilst they are both zero, you have been trusted with £20k in total, again your scoring will be based on how the account was maintained.
If a lender comes along, mortgage/car finance for instance, they would look at 3 areas, the amount of "trust" (Credit Limit) given by the card company, the conduct of the account and the balance owed.
The lender would provide a greater level of finance if your account was similar to option 2, because of the increased credit limit. This is not to say that you have the "means" in which to pay, but they'd be more willing to loan based on the "trust" previously given by the card company.
If your "means" are fully consumed, i.e. annual credit of £40k and you're at £35k, then clearly a loan/finance won't be provided.
There's no harm in having two empty cards with huge credit limits. As long as you're not above or near your means, then credit will be supplied without issue. Your scoring will also reflect the same.
My Mrs has a card, she doesn't earn a huge amount, but her credit limit is off the scale, higher than her annual salary. It shows the bank/card company are willing to loan the money due to the conduct of her account/card. He/she who doesn't pay the balances when due, defaults on payments will lose "trust", hold a low credit score and potentially reside at the higher end of their "means" to pay.
I have 3 cards, all with tidy credit limits, not that I use them, but I swap between them for interest free credit, and also boosts my credit score, due to the "trust" / "Performance" / "Means".
If you're a shopaholic then bin the cards! If you have Zeditus, keep the cards, as there's always a rain day for modifications