Heat vegetable oil in a deep-fat fryer to 140C/275F (CAUTION: Hot oil is very dangerous. Do not leave unattended).
For the chips, slice the potatoes into 1.5cm/½in thick long chips.
Carefully place the chips in the hot vegetable oil and cook for 5-6 minutes or until just tender, but without colour.
Remove carefully from the fryer using a metal slotted spoon. Turn up the temperature to 190C/375F.
Carefully place the chips back into the hot vegetable oil and fry for a furthur 3-4 minutes or until golden and cooked through.
Remove from the fryer using a metal slotted spoon and drain on kitchen paper. Season with salt, to taste.
Meanwhile, for the lobster thermidor, cut the lobster in half using a sharp knife. Remove the meat from the claws, tail and head and set aside.
Cut the lobster meat up and place back into the shell.
For the sauce, put the butter in a saucepan over a medium to high heat, add the shallots and fry until softened.
Pour the stock, wine and double cream into the saucepan, bring to the boil and reduce by half.
Add the mustard, herbs and lemon juice to the sauce. Season with sea salt and freshly ground black pepper.
Pre-heat the grill to its highest setting.
Spoon the sauce over the lobster meat and sprinkle with the grated parmesan cheese.
Place onto a tray and under the pre-heated grill for 3-4 minutes until golden brown.
To serve, place half the lobster onto a serving plate and serve alongside the chips.