I currently have a Goldfisdh Mastercard and an MBNA Visa card. I use the Goldfish card and clear any balance off monthly and have a 6.5k credit limit. I never use the MBNA card and recently reduced the limit from 11k to 1k! I am looking to change mortgages next year and read that reducing the credit that I have can increase my credit rating etc. I always thought it was good to keep a Mastercard and a Visa just in case but would I be better off cancelling the MBNA card altogether?

Yes it's better to close any accounts you aren't using because the mortgage company will look at what you have as available credit and assume you could blow the lot at any moment.
I keep one card with a £1000 limit in case of emergencies and chop the rest up and return them as soon as the 0% deal is over.

BTW you have two of the most expensive cards around, the fact that you have been given £6.5k and £11k as credit limits show you are a good credit risk so transfer that last £1000 to a 0% deal and keep the money in your pocket not MBNA's.

Why don't you try the eScrip Visa. I've been looking for a credit card that I can use and still be able to afford to make donations to worthy causes. The Grassroots.org (http://www.grassroots.org) nonprofit Escrip Visa program allows you to use the card and up to 2% of the transactions gets donated back to Grassroots.org. The thing is that Grassroots.org can really use the funding so that they can continue their important outreach. Here is the link to the Grassroots.org Escrip Visa if you are interested: http://www.grassroots.org/sp/eScrip