EIM32070 indicates that even if an employee attends a location only one day a week then it may be deemed a permanent workplace and therefore no tax relief would be allowable.
Even if the employee attends the workplace only on one or two days a week, if it is on a regular basis, the workplace may still be a permanent workplace.
http://www.hmrc.gov.uk/manuals/eimanual/EIM32070.htm
With regard to the "May" bit of the above advise EIM32140 gives some further advise, i would say IF the factors indicate there is a permanence to the work there then it looks likely that relief would not be allowable.
http://www.hmrc.gov.uk/manuals/eimanual/EIM32140.htm
Note if the one day a week at that office is only needed for temporary period that is expected to last than two years (unless its all of the employment) - then there may be much more scope for claiming under the temporary workplace rules - it doesn't sound like this is the case here though.