  Magnetars are a promising candidate for the origin of Fast Radio Bursts
(FRBs). The detection of an extremely luminous radio burst from the Galactic
magnetar SGR J1935+2154 on 2020 April 28 added credence to this hypothesis. We
report on simultaneous and non-simultaneous observing campaigns using the
Arecibo, Effelsberg, LOFAR, MeerKAT, MK2 and Northern Cross radio telescopes
and the MeerLICHT optical telescope in the days and months after the April 28
event. We did not detect any significant single radio pulses down to fluence
limits between 25 mJy ms and 18 Jy ms. Some observing epochs overlapped with
times when X-ray bursts were detected. Radio images made on four days using the
MeerKAT telescope revealed no point-like persistent or transient emission at
the location of the magnetar. No transient or persistent optical emission was
detected over seven days. Using the multi-colour MeerLICHT images combined with
relations between DM, NH and reddening we constrain the distance to SGR
J1935+2154, to be between 1.5 and 6.5 kpc. The upper limit is consistent with
some other distance indicators and suggests that the April 28 burst is closer
to two orders of magnitude less energetic than the least energetic FRBs. The
lack of single-pulse radio detections shows that the single pulses detected
over a range of fluences are either rare, or highly clustered, or both. It may
also indicate that the magnetar lies somewhere between being radio-quiet and
radio-loud in terms of its ability to produce radio emission efficiently.
