Susanna,
A few more thoughts:
1. If you sell the non-ISA holdings immediately, it's worth double-checking where you stand in the current tax year (to 5/4/2013) re other disposals you might have made since 6/4/2012 that are subject to capital gains tax. You can cash in holdings in the tax year without c.g.t. charge if the total PROFITS taken in the year do not exceed £10,600.
It sounds quite probable that you would not have a liability this year from the information you've supplied, however.
2. Once we get to 6/4/2013, a new tax year's cgt allowance becomes available, of £10,900.
3. Your Standard Life shares and Barclays shares are, in my view, relatively, high risk, since they concentrate a fair bit of your investable wealth in the financial services/banking sector, which took a real pasting in 2007, followed by a sharp recovery from 'the pits'.
4. NSCs - these are no longer on sale, so you are holding a rare breed there! I personally would keep them if they are index-linked certificates, as protection against future inflation, but if they are fixed-rate, they are vulnerable to future rises in inflation.
If you are given the chance to roll over the existing certificates into a future issue of index-linked certificates, it's probably worth taking it up.
5. The endowment policy: don't cash it in before maturity, to avoid sacrificing the final bonus (if any). I have been a firm believer in NOT putting money into endowment policies or insurance bonds for about 20 years now, since they are not transparent to the investor, the payouts are controlled by the insurance company, not by the value of the investments held by that insurance company, and the charges are likely to be much higher than what you can achieve much more transparently elsewhere.
6. Mortgages are a minefield these days - so many different types. If you have any choice in the matter, study the options very carefully indeed. Read all terms and conditions, and ask the provider if you don't understand exactly what the benefits and drawbacks are.
7. Mortgages become cheaper if you can overpay and thereby reduce the amount owed faster, and/or reduce the term. Do look at offset mortgages if you have a highish salary coming in, because this type of mortgage allows you to reduce (each month) the outstanding amount on which you have to pay interest that month.
Hope some of the above helps!