  For certain theories of existentially closed topological differential fields,
we show that there is a strong relationship between $\mathcal
L\cup\{D\}$-definable sets and their $\mathcal L$-reducts, where $\mathcal L$
is a relational expansion of the field language and $D$ a symbol for a
derivation. This enables us to associate with an $\mathcal
L\cup\{D\}$-definable group in models of such theories, a local $\mathcal
L$-definable group. As a byproduct, we show that in closed ordered differential
fields, one has the descending chain condition on centralisers.
