Can I buy goods “tax free” when working abroad?

In principle, goods are never “tax free”, but when you are travelling from the EU* to the UK and have purchased some goods in another EU country, you will not have to pay any tax or duty as long as the tax was included when you purchased the items. These products should also be for your own use and should be transported by you to the UK. Gifts are included, but no items that are intended to be used as a payment or to be resold.
Liquor, tobacco and pure perfume are classified as duty free goods and can be brought back into the UK, up to a certain quantity. If you try to import more than the following quantities, the customs officer will certainly question you about your purposes: 3200 cigarettes, 400 cigarillos, 200 cigars, 3 kg of smoking tobacco, 110 litres of beer, 10 litres of spirits, 90 litres of wine, 20 litres of fortified wine( i.e.: port or sherry).

Some exceptions stand for these EU countries:

From Czech Republic - 200 cigarettes or 250g of smoking tobacco or 50 cigars or 100 cigarillos
From Estonia- 200 cigarettes or 250g of smoking tobacco (No limit on other tobacco products as long as they are for your own use.)
From Hungary, Latvia, Lithuania, Poland, Slovakia or Slovenia - 200 cigarettes (No limit on other tobacco products as long as they are for your own use.)

When you are travelling from outside the EU to the UK you are allowed to bring in the following products under the same conditions as above. The quantity is limited as follows: 200 cigarettes; or 100 cigarillos; or 50 cigars; or 250 gm of tobacco; 2 litres of still table wine; 1 litre of spirits or strong liqueurs over 22% volume, or 2 litres of fortified wine, sparkling wine or other liqueurs; 60cc/ml of perfume; 250cc/ml of Eau de toilette; £145 worth of all other goods including gifts and souvenirs.

*The EU countries currently include: Austria, Belgium, Cyprus (Greek part), Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Irish Republic, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Poland, Portugal, Slovakia, Slovenia, Spain (but not the Canary Islands), Sweden and the United Kingdom (but not the Channel Islands).