My advice is that your offer will only ever be negotiated upwards, never downwards.
It sounds like you are in a buyer's market.
To the OP, as Highland Park has said it really is a buyer's (or renters) market at the moment, nationwide. Be bold with your initial offer, undercut the lower end of the asking price significantly and work from there. Get three figures straight in your head: 1. Your dream price (a rental value that you would be delighted with, 2. An upper limit to which you are prepared to go to and 3. An acceptable value, this will fall somewhere inbetween one or two, if the landlord won't budge but comes near this price and you want the property then make the deal.
Remember that these values shouldn't just be educated guesses at what you deem to be acceptable. They should fit in with your projected sales and growth over the tenure of the lease. Make this decision in association with your business plan.
You should also be bold in asking for an initial rent free period. Most landlords are happy just to get the property filled to get some money coming in and in a good deal you can expect to get 3-6 months rent free. Ask for 12 months and let the landlord work you back from there. You should note however that many landlords will expect you to return the favour so if you want 6 months rent free it will likely be the latter 6 months of the rolling year, whilst you remain liable to pay for the first 6 months.
Most landlords will expect a deposit, the value of which varies wildly but is typically based on a multiplication of the monthly rent value eg. deposit = value of 2 months rent. As the saying goes, everything is negotiable.
If you can convince them that your money would serve both parties best if you were able to spend this money on securing the future of your business and as such would keep the property occupied then they might take your point.
Can I ask what condition the units are in? If they are new unit and you are the first occupant, what work will be required to turn it from a shell into a serviceable unit? Has the RCD consumer unit been installed? Has the unit been connected to mains water? etc. Who will be responsible for paying for these to be set up?
If it is an older building, what remedial work will be required and who will pay for it?