Based on your question I assumed:
- The house purchase in question is in England/Northern Ireland (based on your tag, and your mention of 'Stamp Duty' - it is known under a different name in Scotland and Wales)
- You owned the flat you currently hold, either on a mortgage or outright
(Please edit the question if these assumptions are not true)
One-line summary: You will need to pay Stamp Duty Land Tax (SDLT), albeit likely at the standard rate.
The current first-time buyers relief on stamp duty comes with the following eligibility:
Rates if you’re buying your first home
You can claim a discount (relief) so you don’t pay any tax up to £300,000 and 5% on the portion from £300,001 to £500,000.
You’re eligible if:
- you, and anyone else you’re buying with, are first-time buyers
- you complete your purchase on or after 22 November 2017
As you, as per the assumptions, bought a home before, you are not eligible. Instead the standard rate apply, which at the time of writing is:
- Zero for the first £125k
- 2% for the next £125k (i.e. up to £250k)
- 5% for the next £675k (i.e. up to £925k), and so on
Now assuming you did not make any home purchases when you are aboard, you do not need to pay the higher rate SDLT.
If you bought a home when you are aboard, and did not manage to sell it before you came back to the UK and buy a UK home, the higher rate SDLT applies. Though in this case the rules are slightly different (see this GOV.UK page):
There are special rules if you own property with someone else or already own a property outside England, Wales and Northern Ireland.
Use this calculator to get an idea how much SDLT you will need to pay.