Regardless of your tax residency status, you will be liable to UK tax on any rental income you receive which exceeds the deductible expenses, such as those listed here
. As a UK national, you will be entitled to a personal allowance to use against your UK source income. The personal allowance is currently £10,000. As you will be living outside the UK, you may have to have tax deducted at source from your rental income under the non-resident landlord scheme which you can read about here
If you don't sell your house in the UK, there can be no CGT to pay. If you sell it whilst being treated as non-UK resident, any gain will be tax free as far as the UK is concerned so long as you stay abroad for at least five years. I'm no expert on the Egypt tax system so you would need to seek separate advice on that as far as tax on your UK rental income and any capital gains is concerned. Credit will be given for tax paid in one country against the tax due on the same income or gain in the other country.
Antiques and coins are treated as chattels. Take a look at HS293 here
for information on how gains made the sale of chattels are taxed in the UK. The same tax exemption would apply if you sold them as a non-UK resident so long as you remained non-UK resident for at least five years.
Take a look here
for information on determining tax residency. Based on the fact that you don't intend to work in Egypt, you will probably be tax resident in the UK for 2014/15, assuming you leave the UK in the current tax year, due to your having a home in the UK for at least 91 days, you spend at least 30 days in it and you have no home which you own abroad. You will, however, probably qualify for split-year treatment which means that the tax year will be divided into two periods for tax purposes, one when you are living in the UK and one when you are abroad.
For each subsequent tax year, you need to run through the tax residency tests to determine your UK tax residency status.
There is a tax treaty between the UK and Egypt which you can find here
I hope this helps but let me know if you have any further questions.