Showering at Heathrow airport?
 

Planning ahead a bit, but i get back from America at 6am UK time on august 22nd, the day of the Reading festival. The jet lag is going to be awful, but i don't really have time to go home first and if there's one thing i cannot handle, it's going there already dirty. So, i need a shower. I have searched this and found there are showers in the terminal 4 arrivals. I have no idea what terminal i will be arriving in, but after i've gone through security and met up with my mum can we drive over to terminal 4 and still get access to showers? or are they after security? TY :D