Hi, realistically, I think £3500 would be difficult.
Back of a fag packet here but,
Training £1000
Motor £1500 for a cheapo
Wing £1500 second hand
Helmet £100
Not essential but advised
Reserve £400 second hand
GPS / altimeter £100 second hand
Air map of your area £20
Once you have your training and kit, please don't under estimate the potential of needing a new prop or two, or some welding of your frame. Props are £150 - £250 generic wood or carbon.
I think nearer £5000 realistically. Remember, you are young and have all your life to enjoy this. A local pilot to mee is still enjoying his flying and he just turned 70!