Although you have done nothing wrong, banks change their lending criteria to match the economy. It may be that Barclays have too much unsecured lending on their books (and some of it may be expected to go bad). Even though you have a very small chance of not paying a further loan, they simply cannot take the chance. You will notice perhaps that Barclays have some very good savings rate sat the moment. They look like they are trying to increase their cash reserves by taking on lots of new savers. Every borower they take on DECREASES their cahs reserves and means they have to sell another ten savings accounts.
You could easily shop around.
The reason that you are now being harrassed by Barclays regarding a secured loan, is that the secured loan department is a completley different business unit with their own sales targets. They are obviously keener to take the risk. I would stick to your guns and shop around.