Do I NEED a new fuse box?

No, you do not need a new consumer unit. Typical of some trades trying to scare the customer into having a new one. If you have any work done the main earthing, earth bonding to gas, water, and/or oil has to be checked for size and even existence, as for saying it has to be metal etc, yes that's true but only if YOU want it changed in the first place! He can't force you to have one, there are a lot of alternatives available if they are doing electrical work in the kitchen.

New installations must comply with the current BS7671 17th edition. Which states from Janurary 2016 all distribution Boards have to be metal enclosed. Earlier installations only have to comply with their earlier regulation requirement and do not have to comply with this, as long as each circuit has mcb and rcd protection on one or both sides if it is a split load board. On another note ll cables installed by the kitchen fitter(s) (must be minimum part P registered if in UK/Wales) need to be at least 50mm deep in the wall (which is rarely possible) if not all circuits need to be RCD protected. All sockets must be RCD protected anyway. Might be a case your distribution board doesn't have enough space if so you would need an additional sub distribution board (metal) but if it does and has RCD protection then no it does not need to be changed. Just get the electrician to check the torque tightness on each connection point inside the distribution board. All connections inside a distribution board need to be torque tightened using a certified torque screwdriver. Manufacturer will state how tight. Very important this as the reason for moving to metal boards was fires from loose connections. Metal contains the flame and tightness prevents loose connection and fire. They could also just fit an RCD in a metal enclosure next to distribution board to protect board but under fault condition all the circuits in board would be isolated. In a nut shell as long as each circuit that is less then 50mm deep (Sockets have to have RCD protection) in a wall have to have RCD Protection and the mcb/fuse is fit for use on that circuit you Do Not have to change the board.

No you don't, he's talking nonsense.

As above us as electricians hear this more and more as long as the circuits comply with the latest regs and there is a spare way in your existing consumer unit there is no requirement to change the consumer unit to metal. If the consumer unit does require Changing it must be made of a non combustible material eg metal or enclosed within an approved fire rated cabinet, I hope that helps. Regards Kelvin Partridge Iconnect Electrical Solutions Ltd

Again echoing the consensus from above. If the board was to be replaced it would need to be metal. If the existing board is ok and meets regulation then there is no need to change it. There should be a note on the certificate to show this.