Iv a set of fairy lights, Rated Voltage 3v, 15mA, I would like to connect four sets together in series (12v 60ma).I can get uk ac/dc 12V 1A Power. Question1 : Do i need to connect a resistor if so what one. Question2 :Is 12 volts enough. Any advice would be appreciated
Four 3 Volt LEDs connected in series will work diretly from your 12 Volt supply, with no extra components. One such group will draw 15 mA.
You can connect up to 66 such sets in parallel to the same 12 Volt 1 Amp power supply.
Correction: I must have been thinking of incandescent lamps when I wrote the first sentence.
LEDs must always be used with a current-limiting resistor, so you want a group of three LEDs, plus a 200 Ohm resistor to operate from 12 Volts. One group will draw 15 mA. (second sentence is OK)
Your fairy lights are likely 2 AA battery powered string of parallel leds and a single resistor. Super common.
You could, in theory, wire four of these in series, including the resistors, and it should work just fine. You would be better off wiring them in parallel, and use a USB power supply with 3x 1n4001 diodes in series to drop 2.1V from the 5V supply.
If they are LEDs, as they very likely are, then no 12 Volts would not be enough. But it is not likely the set of four LEDs or your supply will be exactly 12v.
You would have to first measure the LED string's forward voltage and find out if they are over or under your supply voltage.
The supply voltage must be higher (not equal) than the LED string's forward voltage.
Once you know the voltages you can calculate the resistor value or use a 50 cent CCR (constant current regulator) like the On-Semi NSV45015WT1G.