Chances are if the pre-meter tails are 16mm2 your meter could do with updating. Ask for a meter change. When they change the meter, they should upgrade the (pre-meter) tails, too. Do what I did if they seem reluctant to change the meter.
Tell them you want to fit an outrageously large electric shower, and as you have three rings and a cooker etc... already, want to be upgraded to a 100A (or better still, 125A) supply.
They offered me an appointment then!!
Was stupid, really. My house was built in 1961, and according to the REC, the meter should have had a 20 year lifespan (making it due for renewal back in 1981), but I'm still stuck with the original 40A meter with rotary dials in 2004. And the b*stards are reluctant to change it even now!!
43 years - good going, huh??