As well as legal constraints relating to planning building regulations and so forth , the landlord will want to ensure that the character and value of his premises are maintained and will require any material alteration to be subject to his approval.

If you have a short term lease, control over alterations will be very strict. Greater flexibility will generally be permitted in a longer term arrangement.

As a prospective long term tenant, you will need to consider: whether there is sufficient flexibility for immediate and longer term business needs; the likely needs of an assignee; and whether alterations will justify a higher rent demand by the landlord at the time of a rent review.

The restraints against alterations may be absolute or alternatively the lease may require you first to obtain the landlord's consent. If the alteration can be considered an improvement, refusal may well be deemed to be unreasonable giving you the right to proceed regardless.

Generally, making alterations to leased premises without the landlord's consent can be risky and professional advice should be taken before embarking on such action.

The landlord may also insert clauses requiring you, as the tenant:
(1) to remove alterations and reinstate the premises (if required) at the end of the tenancy;
(2) not to tamper with the services applicable to common parts;
(3) not to apply for planning permission without the landlord's consent; and
(4) not to place signs or hoardings on the premises.

At the end of the lease, you may be able to claim compensation from the landlord for improvements if they are beneficial to the premises and prior authorisation from the landlord was obtained. The amount of the claim would normally be either the addition to the value of the premises or the reasonable costs of the improvements. The landlord must pay within three months of the end of the lease, failing which you can seek a Court order enforcing payment.