1 Your accountant is correct. If you make a gain on the sale of assets including your share of the goodwill used in a business which operates in the UK, you are liable to CGT on the gain even if you are non-UK resident. You will, however, probably be eligible for entrepreneurs' relief which would restrict the CGT charge to 10% of the taxable gain. Read about ER in HS275
2 When you cease to be a partner in the business, your tax return should show the date that your status changed and that will impact on your tax liability for the final tax year during which you are a partner. You won't need to make tax payments on account for a tax year after you have left the business unless you have other sources of UK income. You could pay pension contributions to reduce your UK tax liability on your share of any profits.
3 If you reinvest some or all of the proceeds of your share of the business into new business assets, you can effectively defer some or all of the CGT charge but you would lose out on entrepreneurs' relief on the initial deferred gain. Take a look at the business asset rollover relief rules in HS290
. Entrepreneurs' relief may be available on the gain on a disposal of the new business.
As far as stock market businesses are concerned, you cannot defer CGT by buying shares in companies such as Barclays or Marks and Spencer. You can defer or eliminate CGT by investing in Enterprise Investment Scheme shares or Seed Enterprise Investment Scheme shares. These would be high risk investments, hence the tax breaks, and are really aimed at those who can afford to lose all of their investment. Read about EIS and SEIS here
4 If you work in the UK, you would have to pay UK tax but only if your UK source income exceeded the personal allowance for the tax year concerned.
I hope this helps but let me know if you have any further questions.