The loan offer letter from the bank most likely includes a clause indicating that the loan offer is dependent on contracts signed for the sale of the first property (based on the info in your last post).
That being the case, your solicitor cannot let you sign the offer letter, until you have the contract sorted out on your sale.
You can of course go back to the bank and get a revised offer letter. You probably will qualify, but it will take T I M E.
¬ Revised application form for mortgage,
¬ amendments possibly being required in planned life cover (which means possibly having to retrieve the policy from your bank, getting it to the life company for them to make the amendments
¬ possibility that your new increased life cover will go over an underwriting limit and while you may have escaped PMA first time, you may now need a PMA (from GP) and this is never quick.
¬ You may be hit with higher repayment rate because rates are usually tied to LTV (which for you looks like more than doubling)
Yes it is possible, but don't think for a minute that the logistics of getting a loan offer changed are straight forward. Been there, and it worked out, but it took best part of 5 weeks.