Don't want to sound harsh but if I was on the cards, only working 37.5 hours a week, being paid for holidays & bank holidays, getting sick pay and pension benefits, had my gas paid for, was getting transport and fuel and had just negotiated another £1200 a year pay rise I wouldn't be too bothered about how much the joiner was getting paid!!.
If you think your hard done by try going self employed, buy/lease a van, pay for your own insurances and fuel, pay for your own gas/G3/water regs and other training/qualifications, sort your own tax (and vat), only get statutory sick pay if your ill, don't earn anything if you take a holiday, find your own work, spend your weekends and evenings preparing quotes, source your own materials, negotiate with merchants/suppliers, buy all your own tools and just hope the work keeps coming and you can make a profit, or at least break even!.
Hope this makes you feel a little happier !