The extent of the works required by your landlord in order for them to issue their consent for the lease to be assigned does, on the face of what you say, appear to be
unreasonable. The starting point, however, is to look at what happened when you took assignment of the lease.
When you took assignment, the previous lessee will have had a schedule of condition carried out by a surveyor, for which the dilapidations report, or schedule of required works, would have been determined. Basically, this is what has now happened to you as the incumbent lessee.
Ask your agent to check your lease to establish precisely what obligations it places upon you in respect of repairs and maintenance. Most leases require you to maintain the property in at least as good a condition as it was when you took on the lease, ensuring ongoing repairs and maintenance works are carried out in order to prevent deterioration in the property's overall state of repair and decorative order.
If elements of the work you are being asked to complete now needed doing when you took the lease on, but were not required at the time, it is unreasonable for you to be saddled with completing them now. In order to establish this, you must refer to the surveyor's schedule of condition and/or dilapidations report completed when you took assignment.
You also need to check on whether the lease places upon you the obligation to ensure the premises are fully compliant with prevailing health and safety requirements and any other legislative requirements affecting the operational status of the premises. If it does, these works must be completed. Check your lease and original schedule of conditions.