http://www.exo-terra.com/en/products/linear_fluorescent_bulbs.php and what fitting could I use for them?
If you are going with a standard T-8 bulb like the ones in the link, the 2.0 and 5.0 put out very little UV. 10.0 is the only choice if providing UV is your goal. Note that you must mount the bulb no more than 10-12" over the tortoise and even then that 10.0 bulb makes pretty weak UV. Using a reflector hood will help.
The newer T-5 HO bulbs from Arcadia and other manufacturers produce A LOT more UV and must be mounted farther away from the tortoise. Find them here: http://www.lightyourreptiles.com
This guy imports them from somewhere in Europe, so I'm sure you could find the Arcadia brand in London.
My Arcadia bulbs are still going strong and making great UV after 2+ years.
A UV meter is essential in placing your bulbs correctly and making sure that you are providing enough UV in a climate like yours where the tortoise is inside most of the year. Like this: https://www.solarmeter.com/model65....t=6.5UVIndex&gclid=CKn7gPD8ztMCFdu3wAodMbUIyg
The meter may seem expensive at first glance, but I would argue that it will save you a ton of money in the long term since you are not replacing bulbs every six months that are working perfectly fine. It also has the added benefit of making sure your tortoise is getting what it needs. This meter is much cheaper than trying to treat MBD, not to mention the suffering a tortoise would endure.
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