During the reign of George II, British Coins with "Britannia" on them would have been either a copper Halfpenny or a Farthing.
A British 1735 copper Farthing (George II), circulated but still in good condition, might fetch anything from £10 to £275 GBP.
A British 1735 copper Farthing (3 over 5)(George II), circulated but still in good condition, might fetch anything from £20 to £380 GBP.
A British 1735 copper Halfpenny (George II), circulated but still in good condition, might fetch anything from £12 to £330 GBP.
NOTE - The reverse of these coins is upside down to the obverse. This is normal.
The values quoted are the best possible for the best specimens in their grades, but may be significantly lower due to varying demand for the coin and the prevailing economic climate. A reputable coin dealer will be able to give a more accurate valuation based on inspection of the coin.
The same as every other 2-headed or 2-tailed "magician's coin" - a couple of bucks as a novelty item but no collector value because it's a privately-made trick coin.
You need to give us a bit more information, particularly what is the main motif on the coin (Britannia, a shield, etc.) and an estimate of what the coin is made out of (gold, silver, copper, etc.) and then we can better identify what it is and hopefully get you a value.
Please check your coin. Queen Anne was on the throne on in 1709, George I did not come to the throne until 1714.
Britannia can be found on the reverse of a Britishnon-commemorative 50 pence piece. Britannia also appeared on predecimal Pennies and pre-1936 Halfpennies.
You have a British coin ("Georgius IV D.G. Britannia Rex F.D." is abbreviated latin for "George the Fourth, King of Britain and Defender of the Faith") dated 1821. To get a value, the denomination and condition of the coin would need to be known.
Other than for commemorative 50 Pence coins, Britannia has been on the reverse of the 50 Pence coin since it was first issued in 1969 until 2008 when the new design British coins were issued.
1997 British 50 Pence coins do not have thistles or roses on either side. The 1997 coin has Britannia on the reverse.
Mass produced in East Asia, may not be authentic.
A British 1735 sterling silver Groat (Fourpence)(George II), circulated but still in good condition, might fetch anything from £14 to £75 GBP. NOTE - The reverse of these coins is upside down to the obverse. This is normal. The values quoted are the best possible for the best specimens in their grades, but may be significantly lower due to varying demand for the coin and the prevailing economic climate. A reputable coin dealer will be able to give a more accurate valuation based on inspection of the coin.
If the inscription in total reads GEORGIVS II REX on the obverse, with BRITANNIA on the reverse, your description lines up with a copper coin, but there were no copper coins minted in 1757 and all Pennies prior to 1797 were a small silver coin. You may have a privately minted coin or a medallion.
The only 1857 coin with Queen Victoria and Britannia on opposite sides and roughly the size of a Penny, is a Penny.
1735 as a percent = 1735 * 100% = 173500%